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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">System identification</span></span>
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</style><table class="infobox" style="width:18em; text-align:center; font-size:95%;"><tbody><tr><th colspan="2" class="infobox-above" style="padding-bottom:0.3em; background:transparent; line-height:1.1em; font-size:125%; font-weight:bold;"><a href="Black_box" title="Black box">Black box systems</a></th></tr><tr><td colspan="2" class="infobox-image"><span typeof="mw:File"></span></td></tr><tr><th colspan="2" class="infobox-header" style="background:#E7C6A5;">System</th></tr><tr><td colspan="2" class="infobox-full-data" style="line-height:1.4em;"><a href="Black_box" title="Black box">Black box</a>, <a href="Oracle_machine" title="Oracle machine">Oracle machine</a></td></tr><tr><th colspan="2" class="infobox-header" style="background:#E7C6A5;">Methods and techniques</th></tr><tr><td colspan="2" class="infobox-full-data" style="line-height:1.4em;"><a href="Black-box_testing" title="Black-box testing">Black-box testing</a>, <a href="Blackboxing" title="Blackboxing">Blackboxing</a> <hr></td></tr><tr><th colspan="2" class="infobox-header" style="background:#E7C6A5;">Related techniques</th></tr><tr><td colspan="2" class="infobox-full-data" style="line-height:1.4em;"><a href="Feed_forward_(control)" title="Feed forward (control)">Feed forward</a>, <a href="Obfuscation" title="Obfuscation">Obfuscation</a>, <a href="Pattern_recognition" title="Pattern recognition">Pattern recognition</a>, <a href="White_box_(software_engineering)" title="White box (software engineering)">White box</a>, <a href="White-box_testing" title="White-box testing">White-box testing</a>, <a href="Gray-box_testing" title="Gray-box testing">Gray-box testing</a>, </td></tr><tr><th colspan="2" class="infobox-header" style="background:#E7C6A5;">Fundamentals</th></tr><tr><td colspan="2" class="infobox-full-data" style="line-height:1.4em;"><a href="A_priori_information" class="mw-redirect" title="A priori information"><i>A priori</i> information</a>, <a href="Control_system" title="Control system">Control systems</a>, <a href="Open_system_(systems_theory)" title="Open system (systems theory)">Open systems</a>, <a href="Operations_research" title="Operations research">Operations research</a>, <a href="Thermodynamic_system" title="Thermodynamic system">Thermodynamic systems</a></td></tr><tr><td colspan="2" class="infobox-navbar"><style data-mw-deduplicate="TemplateStyles:r1129693374">
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<p>The field of <b>system identification</b> uses <a href="Statistical_method" class="mw-redirect" title="Statistical method">statistical methods</a> to build <a href="Mathematical_model" title="Mathematical model">mathematical models</a> of <a href="Dynamical_system" title="Dynamical system">dynamical systems</a> from measured data.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> System identification also includes the <a href="Optimal_design" class="mw-redirect" title="Optimal design">optimal</a> <a href="Design_of_experiments" title="Design of experiments">design of experiments</a> for efficiently generating informative data for <a href="Regression_analysis" title="Regression analysis">fitting</a> such models as well as model reduction. A common approach is to start from measurements of the behavior of the system and the external influences (inputs to the system) and try to determine a mathematical relation between them without going into many details of what is actually happening inside the system; this approach is called <b><a href="Black_box_(systems)" class="mw-redirect" title="Black box (systems)">black box</a></b> system identification.
</p>
<meta property="mw:PageProp/toc">
<div class="mw-heading mw-heading2"><h2 id="Overview">Overview</h2></div>
<p>A dynamic mathematical model in this context is a mathematical description of the dynamic behavior of a <a href="System" title="System">system</a> or process in either the time or frequency domain. Examples include:
</p>
<ul><li><a href="Physical_system" title="Physical system">physical</a> processes such as the movement of a falling body under the influence of <a href="Gravity" title="Gravity">gravity</a>;</li>
<li><a href="Economic_system" title="Economic system">economic</a> processes such as international <a href="Trade" title="Trade">trade</a> markets that react to external influences.</li></ul>
<p>One of the many possible applications of system identification is in <a href="Control_theory" title="Control theory">control systems</a>. For example, it is the basis for modern <a href="Data-driven_control_system" title="Data-driven control system">data-driven control systems</a>, in which concepts of system identification are integrated into the controller design, and lay the foundations for formal controller optimality proofs.
</p>
<div class="mw-heading mw-heading3"><h3 id="Input-output_vs_output-only">Input-output vs output-only</h3></div>
<p>System identification techniques can utilize both input and output data (e.g. <a href="Eigensystem_realization_algorithm" title="Eigensystem realization algorithm">eigensystem realization algorithm</a>) or can include only the output data (e.g. <a href="Frequency_domain_decomposition" title="Frequency domain decomposition">frequency domain decomposition</a>). Typically an input-output technique would be more accurate, but the input data is not always available. In addition, the final estimated responses from arbitrary inputs can be analyzed by investigating their correlation and spectral properties.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>
</p>
<div class="mw-heading mw-heading3"><h3 id="Optimal_design_of_experiments">Optimal design of experiments</h3></div>
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</style><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Optimal_design" class="mw-redirect" title="Optimal design">Optimal design §&nbsp;System identification and stochastic approximation</a></div>
<p>The quality of system identification depends on the quality of the inputs, which are under the control of the systems engineer. Therefore, systems engineers have long used the principles of the <a href="Design_of_experiments" title="Design of experiments">design of experiments</a>.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> In recent decades, engineers have increasingly used the theory of <a href="Optimal_design" class="mw-redirect" title="Optimal design">optimal experimental design</a> to specify inputs that yield <a href="Efficient_estimator" class="mw-redirect" title="Efficient estimator">maximally precise</a> <a href="Estimator" title="Estimator">estimators</a>.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup>
</p>
<div class="mw-heading mw-heading2"><h2 id="White-,_grey-,_and_black-box">White-, grey-, and black-box</h2></div>

<p>One could build a <a href="White-box_testing" title="White-box testing">white-box</a> model based on <a href="First_principles" class="mw-redirect" title="First principles">first principles</a>, e.g. a model for a physical process from the <a href="Newton's_laws_of_motion" title="Newton's laws of motion">Newton equations</a>, but in many cases, such models will be overly complex and possibly even impossible to obtain in reasonable time due to the complex nature of many systems and processes.
</p><p>A more common approach is therefore to start from measurements of the behavior of the system and the external influences (inputs to the system) and try to determine a mathematical relation between them without going into the details of what is actually happening inside the system. This approach is called system identification. Two types of models are common in the field of system identification:
</p>
<ul><li><b>grey box model:</b> although the peculiarities of what is going on inside the system are not entirely known, a certain model based on both insight into the system and experimental data is constructed. This model does however still have a number of unknown free <a href="Parameter" title="Parameter">parameters</a> which can be estimated using system identification.<sup id="cite_ref-Nielsen_6-0" class="reference"><a href="#cite_note-Nielsen-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Nielsen2_7-0" class="reference"><a href="#cite_note-Nielsen2-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> One example<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> uses the <a href="Monod_equation" title="Monod equation">Monod saturation model</a> for microbial growth. The model contains a simple hyperbolic relationship between substrate concentration and growth rate, but this can be justified by molecules binding to a substrate without going into detail on the types of molecules or types of binding. Grey box modeling is also known as semi-physical modeling.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup></li>
<li><b><a href="Black_box_(systems)" class="mw-redirect" title="Black box (systems)">black box</a> model:</b> No prior model is available. Most system identification algorithms are of this type.</li></ul>
<p>In the context of <a href="Nonlinear_system_identification" title="Nonlinear system identification">nonlinear system identification</a> Jin et al.<sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> describe grey-box modeling by assuming a model structure a priori and then estimating the model parameters. Parameter estimation is relatively easy if the model form is known but this is rarely the case. Alternatively, the structure or model terms for both linear and highly complex nonlinear models can be identified using <a href="Nonlinear_system_identification#NARMAX_methods" title="Nonlinear system identification">NARMAX</a> methods.<sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> This approach is completely flexible and can be used with grey box models where the algorithms are primed with the known terms, or with completely black-box models where the model terms are selected as part of the identification procedure. Another advantage of this approach is that the algorithms will just select linear terms if the system under study is linear, and nonlinear terms if the system is nonlinear, which allows a great deal of flexibility in the identification.
</p>
<div class="mw-heading mw-heading2"><h2 id="Identification_for_control">Identification for control</h2></div>
<p>In <a href="Control_theory" title="Control theory">control systems</a> applications, the objective of engineers is to obtain a <a href="Control_theory#Control_specification" title="Control theory">good performance</a> of the <a href="Control_theory#Open-loop_and_closed-loop_(feedback)_control" title="Control theory">closed-loop</a> system, which is the one comprising the physical system, the feedback loop and the controller. This performance is typically achieved by designing the control law relying on a model of the system, which needs to be identified starting from experimental data. If the model identification procedure is aimed at control purposes, what really matters is not to obtain the best possible model that fits the data, as in the classical system identification approach, but to obtain a model satisfying enough for the closed-loop performance. This more recent approach is called <b>identification for control</b>, or <b>I4C</b> in short.
</p><p>The idea behind I4C can be better understood by considering the following simple example.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> Consider a system with <i>true</i> <a href="Transfer_function" title="Transfer function">transfer function</a> <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle G_{0}(s)}">
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</p>
<dl><dd><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle G_{0}(s)={\frac {1}{s+1}}}">
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</math></span><img src="./6969b68b954e350601f51dccc98c853933ab1524.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.005ex; width:14.809ex; height:5.343ex;" alt="{\displaystyle G_{0}(s)={\frac {1}{s+1}}}" loading="lazy"></span></dd></dl>
<p>and an identified model <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\hat {G}}(s)}">
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<dl><dd><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\hat {G}}(s)={\frac {1}{s}}.}">
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<p>From a classical system identification perspective, <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\hat {G}}(s)}">
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<annotation encoding="application/x-tex">{\displaystyle {\hat {G}}(s)}</annotation>
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</math></span><img src="./9cadea78a2832d8c2d748d8086387dd6ee839942.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.726ex; height:3.343ex;" alt="{\displaystyle {\hat {G}}(s)}" loading="lazy"></span> is <i>not</i>, in general, a <i>good</i> model for <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle G_{0}(s)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<msub>
<mi>G</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>0</mn>
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</msub>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle G_{0}(s)}</annotation>
</semantics>
</math></span><img src="./1c4851fe8e645084c115fb5aeb2adaa7a2cf1db7.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:5.781ex; height:2.843ex;" alt="{\displaystyle G_{0}(s)}" loading="lazy"></span>. In fact, modulus and phase of <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\hat {G}}(s)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<mrow class="MJX-TeXAtom-ORD">
<mover>
<mi>G</mi>
<mo stretchy="false">^<!-- ^ --></mo>
</mover>
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</mrow>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle {\hat {G}}(s)}</annotation>
</semantics>
</math></span><img src="./9cadea78a2832d8c2d748d8086387dd6ee839942.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.726ex; height:3.343ex;" alt="{\displaystyle {\hat {G}}(s)}" loading="lazy"></span> are different from those of <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle G_{0}(s)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<msub>
<mi>G</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>0</mn>
</mrow>
</msub>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle G_{0}(s)}</annotation>
</semantics>
</math></span><img src="./1c4851fe8e645084c115fb5aeb2adaa7a2cf1db7.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:5.781ex; height:2.843ex;" alt="{\displaystyle G_{0}(s)}" loading="lazy"></span> at low frequency. What is more, while <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle G_{0}(s)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<msub>
<mi>G</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>0</mn>
</mrow>
</msub>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle G_{0}(s)}</annotation>
</semantics>
</math></span><img src="./1c4851fe8e645084c115fb5aeb2adaa7a2cf1db7.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:5.781ex; height:2.843ex;" alt="{\displaystyle G_{0}(s)}" loading="lazy"></span> is an <a href="Lyapunov_stability" title="Lyapunov stability">asymptotically stable</a> system, <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\hat {G}}(s)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<mrow class="MJX-TeXAtom-ORD">
<mover>
<mi>G</mi>
<mo stretchy="false">^<!-- ^ --></mo>
</mover>
</mrow>
</mrow>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle {\hat {G}}(s)}</annotation>
</semantics>
</math></span><img src="./9cadea78a2832d8c2d748d8086387dd6ee839942.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.726ex; height:3.343ex;" alt="{\displaystyle {\hat {G}}(s)}" loading="lazy"></span> is a simply stable system. However, <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\hat {G}}(s)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<mrow class="MJX-TeXAtom-ORD">
<mover>
<mi>G</mi>
<mo stretchy="false">^<!-- ^ --></mo>
</mover>
</mrow>
</mrow>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle {\hat {G}}(s)}</annotation>
</semantics>
</math></span><img src="./9cadea78a2832d8c2d748d8086387dd6ee839942.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.726ex; height:3.343ex;" alt="{\displaystyle {\hat {G}}(s)}" loading="lazy"></span> may still be a model good enough for control purposes. In fact, if one wants to apply a <a href="PID_controller" class="mw-redirect" title="PID controller">purely proportional</a> <a href="Negative_feedback" title="Negative feedback">negative feedback</a> controller with high gain <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle K}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>K</mi>
</mstyle>
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<annotation encoding="application/x-tex">{\displaystyle K}</annotation>
</semantics>
</math></span><img src="./2b76fce82a62ed5461908f0dc8f037de4e3686b0.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:2.066ex; height:2.176ex;" alt="{\displaystyle K}" loading="lazy"></span>, the closed-loop transfer function from the reference to the output is, for <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle G_{0}(s)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<msub>
<mi>G</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>0</mn>
</mrow>
</msub>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle G_{0}(s)}</annotation>
</semantics>
</math></span><img src="./1c4851fe8e645084c115fb5aeb2adaa7a2cf1db7.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:5.781ex; height:2.843ex;" alt="{\displaystyle G_{0}(s)}" loading="lazy"></span>
</p>
<dl><dd><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {KG_{0}(s)}{1+KG_{0}(s)}}={\frac {K}{s+1+K}}}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<mfrac>
<mrow>
<mi>K</mi>
<msub>
<mi>G</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>0</mn>
</mrow>
</msub>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mrow>
<mrow>
<mn>1</mn>
<mo>+</mo>
<mi>K</mi>
<msub>
<mi>G</mi>
<mrow class="MJX-TeXAtom-ORD">
<mn>0</mn>
</mrow>
</msub>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
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</mfrac>
</mrow>
<mo>=</mo>
<mrow class="MJX-TeXAtom-ORD">
<mfrac>
<mi>K</mi>
<mrow>
<mi>s</mi>
<mo>+</mo>
<mn>1</mn>
<mo>+</mo>
<mi>K</mi>
</mrow>
</mfrac>
</mrow>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle {\frac {KG_{0}(s)}{1+KG_{0}(s)}}={\frac {K}{s+1+K}}}</annotation>
</semantics>
</math></span><img src="./f871e7535f182511beddeec8a90a8938daa73b17.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.671ex; width:26.62ex; height:6.509ex;" alt="{\displaystyle {\frac {KG_{0}(s)}{1+KG_{0}(s)}}={\frac {K}{s+1+K}}}" loading="lazy"></span></dd></dl>
<p>and for <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\hat {G}}(s)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<mrow class="MJX-TeXAtom-ORD">
<mover>
<mi>G</mi>
<mo stretchy="false">^<!-- ^ --></mo>
</mover>
</mrow>
</mrow>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle {\hat {G}}(s)}</annotation>
</semantics>
</math></span><img src="./9cadea78a2832d8c2d748d8086387dd6ee839942.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.726ex; height:3.343ex;" alt="{\displaystyle {\hat {G}}(s)}" loading="lazy"></span>
</p>
<dl><dd><span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {K{\hat {G}}(s)}{1+K{\hat {G}}(s)}}={\frac {K}{s+K}}.}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<mfrac>
<mrow>
<mi>K</mi>
<mrow class="MJX-TeXAtom-ORD">
<mrow class="MJX-TeXAtom-ORD">
<mover>
<mi>G</mi>
<mo stretchy="false">^<!-- ^ --></mo>
</mover>
</mrow>
</mrow>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mrow>
<mrow>
<mn>1</mn>
<mo>+</mo>
<mi>K</mi>
<mrow class="MJX-TeXAtom-ORD">
<mrow class="MJX-TeXAtom-ORD">
<mover>
<mi>G</mi>
<mo stretchy="false">^<!-- ^ --></mo>
</mover>
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</mrow>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mrow>
</mfrac>
</mrow>
<mo>=</mo>
<mrow class="MJX-TeXAtom-ORD">
<mfrac>
<mi>K</mi>
<mrow>
<mi>s</mi>
<mo>+</mo>
<mi>K</mi>
</mrow>
</mfrac>
</mrow>
<mo>.</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle {\frac {K{\hat {G}}(s)}{1+K{\hat {G}}(s)}}={\frac {K}{s+K}}.}</annotation>
</semantics>
</math></span><img src="./9c80f066f300dfd3b1bce62ee1b78f3998bdcf4e.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -3.171ex; width:22.21ex; height:7.509ex;" alt="{\displaystyle {\frac {K{\hat {G}}(s)}{1+K{\hat {G}}(s)}}={\frac {K}{s+K}}.}" loading="lazy"></span></dd></dl>
<p>Since <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle K}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mi>K</mi>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle K}</annotation>
</semantics>
</math></span><img src="./2b76fce82a62ed5461908f0dc8f037de4e3686b0.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:2.066ex; height:2.176ex;" alt="{\displaystyle K}" loading="lazy"></span> is very large, one has that <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle 1+K\approx K}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mn>1</mn>
<mo>+</mo>
<mi>K</mi>
<mo>≈<!-- ≈ --></mo>
<mi>K</mi>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle 1+K\approx K}</annotation>
</semantics>
</math></span><img src="./c2ab72d2e0b37b98fa65b7ced52566bc95b86722.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.505ex; width:11.233ex; height:2.343ex;" alt="{\displaystyle 1+K\approx K}" loading="lazy"></span>. Thus, the two closed-loop transfer functions are indistinguishable. In conclusion, <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\hat {G}}(s)}">
<semantics>
<mrow class="MJX-TeXAtom-ORD">
<mstyle displaystyle="true" scriptlevel="0">
<mrow class="MJX-TeXAtom-ORD">
<mrow class="MJX-TeXAtom-ORD">
<mover>
<mi>G</mi>
<mo stretchy="false">^<!-- ^ --></mo>
</mover>
</mrow>
</mrow>
<mo stretchy="false">(</mo>
<mi>s</mi>
<mo stretchy="false">)</mo>
</mstyle>
</mrow>
<annotation encoding="application/x-tex">{\displaystyle {\hat {G}}(s)}</annotation>
</semantics>
</math></span><img src="./9cadea78a2832d8c2d748d8086387dd6ee839942.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:4.726ex; height:3.343ex;" alt="{\displaystyle {\hat {G}}(s)}" loading="lazy"></span> is a <i>perfectly acceptable</i> identified model for the <i>true</i> system if such feedback control law has to be applied. Whether or not a model is <i>appropriate</i> for control design depends not only on the plant/model mismatch but also on the controller that will be implemented. As such, in the I4C framework, given a control performance objective, the control engineer has to design the identification phase in such a way that the performance achieved by the model-based controller on the <i>true</i> system is as high as possible.
</p><p>Sometimes, it is even more convenient to design a controller without explicitly identifying a model of the system, but directly working on experimental data. This is the case of <i>direct</i> <a href="Data-driven_control_system" title="Data-driven control system">data-driven control systems</a>.
</p>
<div class="mw-heading mw-heading2"><h2 id="Forward_model">Forward model</h2></div>
<p>A common understanding in Artificial Intelligence is that the <a href="Controller_(control_theory)" class="mw-redirect" title="Controller (control theory)">controller</a> has to generate the next move for a <a href="Robot" title="Robot">robot</a>. For example, the robot starts in the maze and then the robot decides to move forward. Model predictive control determines the next action indirectly. The term <a href="Mathematical_model" title="Mathematical model">"model"</a> is referencing to a forward model which doesn't provide the correct action but simulates a scenario.<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> A forward model is equal to a <a href="Physics_engine" title="Physics engine">physics engine</a> used in game programming. The model takes an input and calculates the future state of the system.
</p><p>The reason why dedicated forward models are constructed is because it allows one to divide the overall control process. The first question is how to predict the future states of the system. That means, to simulate a <a href="Plant_(control_theory)" title="Plant (control theory)">plant</a> over a timespan for different input values. And the second task is to search for a <a href="Sequence_of_events" class="mw-redirect" title="Sequence of events">sequence</a> of input values which brings the plant into a goal state. This is called predictive control.
</p><p>The forward model is the most important aspect of a <a href="Model_predictive_control" title="Model predictive control">MPC-controller</a>. It has to be created before the <a href="Solver" title="Solver">solver</a> can be realized. If it's unclear what the behavior of a system is, it's not possible to search for meaningful actions. The workflow for creating a forward model is called system identification. The idea is to <a href="Formal_system" title="Formal system">formalize a system</a> in a set of equations which will behave like the original system.<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> The error between the real system and the forward model can be measured.
</p><p>There are many techniques available to create a forward model: <a href="Ordinary_differential_equation" title="Ordinary differential equation">ordinary differential equations</a> is the classical one which is used in <a href="Physics_engine" title="Physics engine">physics engines</a> like <a href="Box2D" title="Box2D">Box2D</a>. A more recent technique is a <a href="Neural_network" title="Neural network">neural network</a> for creating the forward model.<sup id="cite_ref-15" class="reference"><a href="#cite_note-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup>
</p>
<div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2></div>
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<ul><li><a href="Black_box_model_of_power_converter" title="Black box model of power converter">Black box model of power converter</a></li>
<li><a href="Black_box" title="Black box">Black box</a></li>
<li><a href="Data-driven_control_system" title="Data-driven control system">Data-driven control system</a></li>
<li><a href="Generalized_filtering" title="Generalized filtering">Generalized filtering</a></li>
<li><a href="Grey_box_completion_and_validation" class="mw-redirect" title="Grey box completion and validation">Grey box completion and validation</a></li>
<li><a href="Hysteresis" title="Hysteresis">Hysteresis</a></li>
<li><a href="LTI_system_theory" class="mw-redirect" title="LTI system theory">Linear time-invariant system theory</a></li>
<li><a href="Model_order_reduction" title="Model order reduction">Model order reduction</a></li>
<li><a href="Model_selection" title="Model selection">Model selection</a></li>
<li><a href="Nonlinear_autoregressive_exogenous_model" title="Nonlinear autoregressive exogenous model">Nonlinear autoregressive exogenous model</a></li>
<li><a href="Open_system_(systems_theory)" title="Open system (systems theory)">Open system (systems theory)</a></li>
<li><a href="Parameter_estimation" class="mw-redirect" title="Parameter estimation">Parameter estimation</a></li>
<li><a href="Pattern_recognition" title="Pattern recognition">Pattern recognition</a></li>
<li><a href="Structural_identifiability" title="Structural identifiability">Structural identifiability</a></li>
<li><a href="System_dynamics" title="System dynamics">System dynamics</a></li>
<li><a href="System_realization" class="mw-redirect" title="System realization">System realization</a></li>
<li><a href="Systems_theory" title="Systems theory">Systems theory</a></li></ul>
</div>
<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>
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</style><cite id="CITEREFTorstenStoica1989" class="citation book cs1">Torsten, Söderström; <a href="Peter_Stoica" title="Peter Stoica">Stoica, P.</a> (1989). <i>System identification</i>. New York: Prentice Hall. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a>&nbsp;<bdi>978-0138812362</bdi>. <a href="OCLC_(identifier)" class="mw-redirect" title="OCLC (identifier)">OCLC</a>&nbsp;<a rel="nofollow" class="external text" href="https://search.worldcat.org/oclc/16983523">16983523</a>.</cite></span>
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</li>
</ol></div></div>
<div class="mw-heading mw-heading2"><h2 id="Further_reading">Further reading</h2></div>
<ul><li><cite id="CITEREFGoodwin,_Graham_C.Payne,_Robert_L.1977" class="citation book cs1">Goodwin, Graham C. &amp; Payne, Robert L. (1977). <i>Dynamic System Identification: Experiment Design and Data Analysis</i>. Academic Press.</cite></li>
<li>Daniel Graupe: <i>Identification of Systems</i>, Van Nostrand Reinhold, New York, 1972 (2nd ed., Krieger Publ. Co., Malabar, FL, 1976)</li>
<li>Eykhoff, Pieter: <i>System Identification – Parameter and System Estimation</i>, John Wiley &amp; Sons, New York, 1974. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a>&nbsp;<bdi>0-471-24980-7</bdi></li>
<li><a href="Lennart_Ljung_(engineer)" title="Lennart Ljung (engineer)">Lennart Ljung</a>: <i>System Identification — Theory For the User</i>, 2nd ed, PTR <a href="Prentice_Hall" title="Prentice Hall">Prentice Hall</a>, Upper Saddle River, N.J., 1999.</li>
<li>Jer-Nan Juang: <i>Applied System Identification</i>, Prentice-Hall, Upper Saddle River, N.J., 1994.</li>
<li><cite id="CITEREFKushner,_Harold_J._and_Yin,_G._George2003" class="citation book cs1"><a href="Harold_J._Kushner" title="Harold J. Kushner">Kushner, Harold J.</a> and Yin, G. George (2003). <i>Stochastic Approximation and Recursive Algorithms and Applications</i> (Second&nbsp;ed.). Springer.</cite><span class="cs1-maint citation-comment"><code class="cs1-code">{{cite book}}</code>: CS1 maint: multiple names: authors list (link)</span></li>
<li>Oliver Nelles: <i>Nonlinear System Identification</i>, Springer, 2001. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a>&nbsp;<bdi>3-540-67369-5</bdi></li>
<li>T. Söderström, <a href="Peter_Stoica" title="Peter Stoica">P. Stoica</a>, System Identification, Prentice Hall, Upper Saddle River, N.J., 1989. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a>&nbsp;<bdi>0-13-881236-5</bdi></li>
<li>R. Pintelon, J. Schoukens, <i>System Identification: A Frequency Domain Approach</i>, 2nd Edition, IEEE Press, Wiley, New York, 2012. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a>&nbsp;<bdi>978-0-470-64037-1</bdi></li>
<li>Spall, J. C. (2003), <i>Introduction to Stochastic Search and Optimization: Estimation, Simulation, and Control</i>, Wiley, Hoboken, NJ.</li>
<li><cite id="CITEREFWalter,_ÉricPronzato,_Luc1997" class="citation book cs1">Walter, Éric &amp; Pronzato, Luc (1997). <i>Identification of Parametric Models from Experimental Data</i>. Springer.</cite></li></ul>
<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>
<ul><li><a rel="nofollow" class="external text" href="http://www.control.isy.liu.se/~ljung/seoul2dvinew/plenary2.pdf">L. Ljung: Perspectives on System Identification, July 2008</a></li>
<li><a rel="nofollow" class="external text" href="http://gramian.de">System Identification and Model Reduction via Empirical Gramians</a></li></ul>
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</style></div><div role="navigation" class="navbox" aria-labelledby="Statistics654" style="padding:3px"><table class="nowraplinks hlist mw-collapsible mw-collapsed navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Statistics654" style="font-size:114%;margin:0 4em"><a href="Statistics" title="Statistics">Statistics</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div>
<ul><li><a href="Outline_of_statistics" title="Outline of statistics">Outline</a></li>
<li><a href="List_of_statistics_articles" title="List of statistics articles">Index</a></li></ul>
</div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Descriptive_statistics654" style="font-size:114%;margin:0 4em"><a href="Descriptive_statistics" title="Descriptive statistics">Descriptive statistics</a></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Continuous_probability_distribution" class="mw-redirect" title="Continuous probability distribution">Continuous data</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Central_tendency" title="Central tendency">Center</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Mean" title="Mean">Mean</a>
<ul><li><a href="Arithmetic_mean" title="Arithmetic mean">Arithmetic</a></li>
<li><a href="Arithmetic%E2%80%93geometric_mean" title="Arithmetic–geometric mean">Arithmetic-Geometric</a></li>
<li><a href="Contraharmonic_mean" title="Contraharmonic mean">Contraharmonic</a></li>
<li><a href="Cubic_mean" title="Cubic mean">Cubic</a></li>
<li><a href="Generalized_mean" title="Generalized mean">Generalized/power</a></li>
<li><a href="Geometric_mean" title="Geometric mean">Geometric</a></li>
<li><a href="Harmonic_mean" title="Harmonic mean">Harmonic</a></li>
<li><a href="Heronian_mean" title="Heronian mean">Heronian</a></li>
<li><a href="Heinz_mean" title="Heinz mean">Heinz</a></li>
<li><a href="Lehmer_mean" title="Lehmer mean">Lehmer</a></li></ul></li>
<li><a href="Median" title="Median">Median</a></li>
<li><a href="Mode_(statistics)" title="Mode (statistics)">Mode</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Statistical_dispersion" title="Statistical dispersion">Dispersion</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Average_absolute_deviation" title="Average absolute deviation">Average absolute deviation</a></li>
<li><a href="Coefficient_of_variation" title="Coefficient of variation">Coefficient of variation</a></li>
<li><a href="Interquartile_range" title="Interquartile range">Interquartile range</a></li>
<li><a href="Percentile" title="Percentile">Percentile</a></li>
<li><a href="Range_(statistics)" title="Range (statistics)">Range</a></li>
<li><a href="Standard_deviation" title="Standard deviation">Standard deviation</a></li>
<li><a href="Variance#Sample_variance" title="Variance">Variance</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Shape_of_the_distribution" class="mw-redirect" title="Shape of the distribution">Shape</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Central_limit_theorem" title="Central limit theorem">Central limit theorem</a></li>
<li><a href="Moment_(mathematics)" title="Moment (mathematics)">Moments</a>
<ul><li><a href="Kurtosis" title="Kurtosis">Kurtosis</a></li>
<li><a href="L-moment" title="L-moment">L-moments</a></li>
<li><a href="Skewness" title="Skewness">Skewness</a></li></ul></li></ul>
</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Count_data" title="Count data">Count data</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Index_of_dispersion" title="Index of dispersion">Index of dispersion</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em">Summary tables</th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Contingency_table" title="Contingency table">Contingency table</a></li>
<li><a href="Frequency_distribution" class="mw-redirect" title="Frequency distribution">Frequency distribution</a></li>
<li><a href="Grouped_data" title="Grouped data">Grouped data</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Correlation_and_dependence" class="mw-redirect" title="Correlation and dependence">Dependence</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Partial_correlation" title="Partial correlation">Partial correlation</a></li>
<li><a href="Pearson_correlation_coefficient" title="Pearson correlation coefficient">Pearson product-moment correlation</a></li>
<li><a href="Rank_correlation" title="Rank correlation">Rank correlation</a>
<ul><li><a href="Kendall_rank_correlation_coefficient" title="Kendall rank correlation coefficient">Kendall's τ</a></li>
<li><a href="Spearman's_rank_correlation_coefficient" title="Spearman's rank correlation coefficient">Spearman's ρ</a></li></ul></li>
<li><a href="Scatter_plot" title="Scatter plot">Scatter plot</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Statistical_graphics" title="Statistical graphics">Graphics</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Bar_chart" title="Bar chart">Bar chart</a></li>
<li><a href="Biplot" title="Biplot">Biplot</a></li>
<li><a href="Box_plot" title="Box plot">Box plot</a></li>
<li><a href="Control_chart" title="Control chart">Control chart</a></li>
<li><a href="Correlogram" title="Correlogram">Correlogram</a></li>
<li><a href="Fan_chart_(statistics)" title="Fan chart (statistics)">Fan chart</a></li>
<li><a href="Forest_plot" title="Forest plot">Forest plot</a></li>
<li><a href="Histogram" title="Histogram">Histogram</a></li>
<li><a href="Pie_chart" title="Pie chart">Pie chart</a></li>
<li><a href="Q%E2%80%93Q_plot" title="Q–Q plot">Q–Q plot</a></li>
<li><a href="Radar_chart" title="Radar chart">Radar chart</a></li>
<li><a href="Run_chart" title="Run chart">Run chart</a></li>
<li><a href="Scatter_plot" title="Scatter plot">Scatter plot</a></li>
<li><a href="Stem-and-leaf_display" title="Stem-and-leaf display">Stem-and-leaf display</a></li>
<li><a href="Violin_plot" title="Violin plot">Violin plot</a></li></ul>
</div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Data_collection654" style="font-size:114%;margin:0 4em"><a href="Data_collection" title="Data collection">Data collection</a></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Design_of_experiments" title="Design of experiments">Study design</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Effect_size" title="Effect size">Effect size</a></li>
<li><a href="Missing_data" title="Missing data">Missing data</a></li>
<li><a href="Optimal_design" class="mw-redirect" title="Optimal design">Optimal design</a></li>
<li><a href="Statistical_population" title="Statistical population">Population</a></li>
<li><a href="Replication_(statistics)" title="Replication (statistics)">Replication</a></li>
<li><a href="Sample_size_determination" title="Sample size determination">Sample size determination</a></li>
<li><a href="Statistic" title="Statistic">Statistic</a></li>
<li><a href="Statistical_power" class="mw-redirect" title="Statistical power">Statistical power</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Survey_methodology" title="Survey methodology">Survey methodology</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Sampling_(statistics)" title="Sampling (statistics)">Sampling</a>
<ul><li><a href="Cluster_sampling" title="Cluster sampling">Cluster</a></li>
<li><a href="Stratified_sampling" title="Stratified sampling">Stratified</a></li></ul></li>
<li><a href="Opinion_poll" title="Opinion poll">Opinion poll</a></li>
<li><a href="Questionnaire" title="Questionnaire">Questionnaire</a></li>
<li><a href="Standard_error" title="Standard error">Standard error</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Experiment" title="Experiment">Controlled experiments</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Blocking_(statistics)" title="Blocking (statistics)">Blocking</a></li>
<li><a href="Factorial_experiment" title="Factorial experiment">Factorial experiment</a></li>
<li><a href="Interaction_(statistics)" title="Interaction (statistics)">Interaction</a></li>
<li><a href="Random_assignment" title="Random assignment">Random assignment</a></li>
<li><a href="Randomized_controlled_trial" title="Randomized controlled trial">Randomized controlled trial</a></li>
<li><a href="Randomized_experiment" title="Randomized experiment">Randomized experiment</a></li>
<li><a href="Scientific_control" title="Scientific control">Scientific control</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em">Adaptive designs</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Adaptive_clinical_trial" class="mw-redirect" title="Adaptive clinical trial">Adaptive clinical trial</a></li>
<li><a href="Stochastic_approximation" title="Stochastic approximation">Stochastic approximation</a></li>
<li><a href="Up-and-Down_Designs" class="mw-redirect" title="Up-and-Down Designs">Up-and-down designs</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Observational_study" title="Observational study">Observational studies</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Cohort_study" title="Cohort study">Cohort study</a></li>
<li><a href="Cross-sectional_study" title="Cross-sectional study">Cross-sectional study</a></li>
<li><a href="Natural_experiment" title="Natural experiment">Natural experiment</a></li>
<li><a href="Quasi-experiment" title="Quasi-experiment">Quasi-experiment</a></li></ul>
</div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Statistical_inference654" style="font-size:114%;margin:0 4em"><a href="Statistical_inference" title="Statistical inference">Statistical inference</a></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Statistical_theory" title="Statistical theory">Statistical theory</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Population_(statistics)" class="mw-redirect" title="Population (statistics)">Population</a></li>
<li><a href="Statistic" title="Statistic">Statistic</a></li>
<li><a href="Probability_distribution" title="Probability distribution">Probability distribution</a></li>
<li><a href="Sampling_distribution" title="Sampling distribution">Sampling distribution</a>
<ul><li><a href="Order_statistic" title="Order statistic">Order statistic</a></li></ul></li>
<li><a href="Empirical_distribution_function" title="Empirical distribution function">Empirical distribution</a>
<ul><li><a href="Density_estimation" title="Density estimation">Density estimation</a></li></ul></li>
<li><a href="Statistical_model" title="Statistical model">Statistical model</a>
<ul><li><a href="Model_specification" class="mw-redirect" title="Model specification">Model specification</a></li>
<li><a href="Lp_space" title="Lp space">L<sup><i>p</i></sup> space</a></li></ul></li>
<li><a href="Statistical_parameter" title="Statistical parameter">Parameter</a>
<ul><li><a href="Location_parameter" title="Location parameter">location</a></li>
<li><a href="Scale_parameter" title="Scale parameter">scale</a></li>
<li><a href="Shape_parameter" title="Shape parameter">shape</a></li></ul></li>
<li><a href="Parametric_statistics" title="Parametric statistics">Parametric family</a>
<ul><li><a href="Likelihood_function" title="Likelihood function">Likelihood</a>&nbsp;<a href="Monotone_likelihood_ratio" title="Monotone likelihood ratio"><span style="font-size: 85%;">(monotone)</span></a></li>
<li><a href="Location%E2%80%93scale_family" title="Location–scale family">Location–scale family</a></li>
<li><a href="Exponential_family" title="Exponential family">Exponential family</a></li></ul></li>
<li><a href="Completeness_(statistics)" title="Completeness (statistics)">Completeness</a></li>
<li><a href="Sufficient_statistic" title="Sufficient statistic">Sufficiency</a></li>
<li><a href="Plug-in_principle" class="mw-redirect" title="Plug-in principle">Statistical functional</a>
<ul><li><a href="Bootstrapping_(statistics)" title="Bootstrapping (statistics)">Bootstrap</a></li>
<li><a href="U-statistic" title="U-statistic">U</a></li>
<li><a href="V-statistic" title="V-statistic">V</a></li></ul></li>
<li><a href="Optimal_decision" title="Optimal decision">Optimal decision</a>
<ul><li><a href="Loss_function" title="Loss function">loss function</a></li></ul></li>
<li><a href="Efficiency_(statistics)" title="Efficiency (statistics)">Efficiency</a></li>
<li><a href="Statistical_distance" title="Statistical distance">Statistical distance</a>
<ul><li><a href="Divergence_(statistics)" title="Divergence (statistics)">divergence</a></li></ul></li>
<li><a href="Asymptotic_theory_(statistics)" title="Asymptotic theory (statistics)">Asymptotics</a></li>
<li><a href="Robust_statistics" title="Robust statistics">Robustness</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Frequentist_inference" title="Frequentist inference">Frequentist inference</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Point_estimation" title="Point estimation">Point estimation</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Estimating_equations" title="Estimating equations">Estimating equations</a>
<ul><li><a href="Maximum_likelihood" class="mw-redirect" title="Maximum likelihood">Maximum likelihood</a></li>
<li><a href="Method_of_moments_(statistics)" title="Method of moments (statistics)">Method of moments</a></li>
<li><a href="M-estimator" title="M-estimator">M-estimator</a></li>
<li><a href="Minimum_distance_estimation" class="mw-redirect" title="Minimum distance estimation">Minimum distance</a></li></ul></li>
<li><a href="Bias_of_an_estimator" title="Bias of an estimator">Unbiased estimators</a>
<ul><li><a href="Minimum-variance_unbiased_estimator" title="Minimum-variance unbiased estimator">Mean-unbiased minimum-variance</a>
<ul><li><a href="Rao%E2%80%93Blackwell_theorem" title="Rao–Blackwell theorem">Rao–Blackwellization</a></li>
<li><a href="Lehmann%E2%80%93Scheff%C3%A9_theorem" title="Lehmann–Scheffé theorem">Lehmann–Scheffé theorem</a></li></ul></li>
<li><a href="Median-unbiased_estimator" class="mw-redirect" title="Median-unbiased estimator">Median unbiased</a></li></ul></li>
<li><a href="Plug-in_principle" class="mw-redirect" title="Plug-in principle">Plug-in</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Interval_estimation" title="Interval estimation">Interval estimation</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Confidence_interval" title="Confidence interval">Confidence interval</a></li>
<li><a href="Pivotal_quantity" title="Pivotal quantity">Pivot</a></li>
<li><a href="Likelihood_interval" class="mw-redirect" title="Likelihood interval">Likelihood interval</a></li>
<li><a href="Prediction_interval" title="Prediction interval">Prediction interval</a></li>
<li><a href="Tolerance_interval" title="Tolerance interval">Tolerance interval</a></li>
<li><a href="Resampling_(statistics)" title="Resampling (statistics)">Resampling</a>
<ul><li><a href="Bootstrapping_(statistics)" title="Bootstrapping (statistics)">Bootstrap</a></li>
<li><a href="Jackknife_resampling" title="Jackknife resampling">Jackknife</a></li></ul></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Statistical_hypothesis_testing" class="mw-redirect" title="Statistical hypothesis testing">Testing hypotheses</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="One-_and_two-tailed_tests" title="One- and two-tailed tests">1- &amp; 2-tails</a></li>
<li><a href="Power_(statistics)" title="Power (statistics)">Power</a>
<ul><li><a href="Uniformly_most_powerful_test" title="Uniformly most powerful test">Uniformly most powerful test</a></li></ul></li>
<li><a href="Permutation_test" title="Permutation test">Permutation test</a>
<ul><li><a href="Randomization_test" class="mw-redirect" title="Randomization test">Randomization test</a></li></ul></li>
<li><a href="Multiple_comparisons" class="mw-redirect" title="Multiple comparisons">Multiple comparisons</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Parametric_statistics" title="Parametric statistics">Parametric tests</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Likelihood-ratio_test" title="Likelihood-ratio test">Likelihood-ratio</a></li>
<li><a href="Score_test" title="Score test">Score/Lagrange multiplier</a></li>
<li><a href="Wald_test" title="Wald test">Wald</a></li></ul>
</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="List_of_statistical_tests" title="List of statistical tests">Specific tests</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><td colspan="2" class="navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Z-test" title="Z-test"><i>Z</i>-test <span style="font-size: 85%;">(normal)</span></a></li>
<li><a href="Student's_t-test" title="Student's t-test">Student's <i>t</i>-test</a></li>
<li><a href="F-test" title="F-test"><i>F</i>-test</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Goodness_of_fit" title="Goodness of fit">Goodness of fit</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Chi-squared_test" title="Chi-squared test">Chi-squared</a></li>
<li><a href="G-test" title="G-test"><i>G</i>-test</a></li>
<li><a href="Kolmogorov%E2%80%93Smirnov_test" title="Kolmogorov–Smirnov test">Kolmogorov–Smirnov</a></li>
<li><a href="Anderson%E2%80%93Darling_test" title="Anderson–Darling test">Anderson–Darling</a></li>
<li><a href="Lilliefors_test" title="Lilliefors test">Lilliefors</a></li>
<li><a href="Jarque%E2%80%93Bera_test" title="Jarque–Bera test">Jarque–Bera</a></li>
<li><a href="Shapiro%E2%80%93Wilk_test" title="Shapiro–Wilk test">Normality <span style="font-size: 85%;">(Shapiro–Wilk)</span></a></li>
<li><a href="Likelihood-ratio_test" title="Likelihood-ratio test">Likelihood-ratio test</a></li>
<li><a href="Model_selection" title="Model selection">Model selection</a>
<ul><li><a href="Cross-validation_(statistics)" title="Cross-validation (statistics)">Cross validation</a></li>
<li><a href="Akaike_information_criterion" title="Akaike information criterion">AIC</a></li>
<li><a href="Bayesian_information_criterion" title="Bayesian information criterion">BIC</a></li></ul></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Rank_statistics" class="mw-redirect" title="Rank statistics">Rank statistics</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Sign_test" title="Sign test">Sign</a>
<ul><li><a href="Sample_median" class="mw-redirect" title="Sample median">Sample median</a></li></ul></li>
<li><a href="Wilcoxon_signed-rank_test" title="Wilcoxon signed-rank test">Signed rank <span style="font-size: 85%;">(Wilcoxon)</span></a>
<ul><li><a href="Hodges%E2%80%93Lehmann_estimator" title="Hodges–Lehmann estimator">Hodges–Lehmann estimator</a></li></ul></li>
<li><a href="Mann%E2%80%93Whitney_U_test" title="Mann–Whitney U test">Rank sum <span style="font-size: 85%;">(Mann–Whitney)</span></a></li>
<li><a href="Nonparametric_statistics" title="Nonparametric statistics">Nonparametric</a> <a href="Analysis_of_variance" title="Analysis of variance">anova</a>
<ul><li><a href="Kruskal%E2%80%93Wallis_test" title="Kruskal–Wallis test">1-way <span style="font-size: 85%;">(Kruskal–Wallis)</span></a></li>
<li><a href="Friedman_test" title="Friedman test">2-way <span style="font-size: 85%;">(Friedman)</span></a></li>
<li><a href="Jonckheere's_trend_test" title="Jonckheere's trend test">Ordered alternative <span style="font-size: 85%;">(Jonckheere–Terpstra)</span></a></li></ul></li>
<li><a href="Van_der_Waerden_test" title="Van der Waerden test">Van der Waerden test</a></li></ul>
</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Bayesian_inference" title="Bayesian inference">Bayesian inference</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Bayesian_probability" title="Bayesian probability">Bayesian probability</a>
<ul><li><a href="Prior_probability" title="Prior probability">prior</a></li>
<li><a href="Posterior_probability" title="Posterior probability">posterior</a></li></ul></li>
<li><a href="Credible_interval" title="Credible interval">Credible interval</a></li>
<li><a href="Bayes_factor" title="Bayes factor">Bayes factor</a></li>
<li><a href="Bayes_estimator" title="Bayes estimator">Bayesian estimator</a>
<ul><li><a href="Maximum_a_posteriori_estimation" title="Maximum a posteriori estimation">Maximum posterior estimator</a></li></ul></li></ul>
</div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="CorrelationRegression_analysis654" style="font-size:114%;margin:0 4em"><div class="hlist"><ul><li><a href="Correlation_and_dependence" class="mw-redirect" title="Correlation and dependence">Correlation</a></li><li><a href="Regression_analysis" title="Regression analysis">Regression analysis</a></li></ul></div></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Correlation_and_dependence" class="mw-redirect" title="Correlation and dependence">Correlation</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Pearson_product-moment_correlation_coefficient" class="mw-redirect" title="Pearson product-moment correlation coefficient">Pearson product-moment</a></li>
<li><a href="Partial_correlation" title="Partial correlation">Partial correlation</a></li>
<li><a href="Confounding" title="Confounding">Confounding variable</a></li>
<li><a href="Coefficient_of_determination" title="Coefficient of determination">Coefficient of determination</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Regression_analysis" title="Regression analysis">Regression analysis</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Errors_and_residuals" title="Errors and residuals">Errors and residuals</a></li>
<li><a href="Regression_validation" title="Regression validation">Regression validation</a></li>
<li><a href="Mixed_model" title="Mixed model">Mixed effects models</a></li>
<li><a href="Simultaneous_equations_model" title="Simultaneous equations model">Simultaneous equations models</a></li>
<li><a href="Multivariate_adaptive_regression_splines" class="mw-redirect" title="Multivariate adaptive regression splines">Multivariate adaptive regression splines (MARS)</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Linear_regression" title="Linear regression">Linear regression</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Simple_linear_regression" title="Simple linear regression">Simple linear regression</a></li>
<li><a href="Ordinary_least_squares" title="Ordinary least squares">Ordinary least squares</a></li>
<li><a href="General_linear_model" title="General linear model">General linear model</a></li>
<li><a href="Bayesian_linear_regression" title="Bayesian linear regression">Bayesian regression</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em">Non-standard predictors</th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Nonlinear_regression" title="Nonlinear regression">Nonlinear regression</a></li>
<li><a href="Nonparametric_regression" title="Nonparametric regression">Nonparametric</a></li>
<li><a href="Semiparametric_regression" title="Semiparametric regression">Semiparametric</a></li>
<li><a href="Isotonic_regression" title="Isotonic regression">Isotonic</a></li>
<li><a href="Robust_regression" title="Robust regression">Robust</a></li>
<li><a href="Homoscedasticity_and_heteroscedasticity" title="Homoscedasticity and heteroscedasticity">Homoscedasticity and Heteroscedasticity</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Generalized_linear_model" title="Generalized linear model">Generalized linear model</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Exponential_family" title="Exponential family">Exponential families</a></li>
<li><a href="Logistic_regression" title="Logistic regression">Logistic <span style="font-size: 85%;">(Bernoulli)</span></a>&nbsp;/ <a href="Binomial_regression" title="Binomial regression">Binomial</a>&nbsp;/ <a href="Poisson_regression" title="Poisson regression">Poisson regressions</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Partition_of_sums_of_squares" title="Partition of sums of squares">Partition of variance</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Analysis_of_variance" title="Analysis of variance">Analysis of variance (ANOVA, anova)</a></li>
<li><a href="Analysis_of_covariance" title="Analysis of covariance">Analysis of covariance</a></li>
<li><a href="Multivariate_analysis_of_variance" title="Multivariate analysis of variance">Multivariate ANOVA</a></li>
<li><a href="Degrees_of_freedom_(statistics)" title="Degrees of freedom (statistics)">Degrees of freedom</a></li></ul>
</div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible mw-collapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Categorical_/_multivariate_/_time-series_/_survival_analysis654" style="font-size:114%;margin:0 4em"><a href="Categorical_variable" title="Categorical variable">Categorical</a>&nbsp;/ <a href="Multivariate_statistics" title="Multivariate statistics">multivariate</a>&nbsp;/ <a href="Time_series" title="Time series">time-series</a>&nbsp;/ <a href="Survival_analysis" title="Survival analysis">survival analysis</a></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Categorical_variable" title="Categorical variable">Categorical</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Cohen's_kappa" title="Cohen's kappa">Cohen's kappa</a></li>
<li><a href="Contingency_table" title="Contingency table">Contingency table</a></li>
<li><a href="Graphical_model" title="Graphical model">Graphical model</a></li>
<li><a href="Poisson_regression" title="Poisson regression">Log-linear model</a></li>
<li><a href="McNemar's_test" title="McNemar's test">McNemar's test</a></li>
<li><a href="Cochran%E2%80%93Mantel%E2%80%93Haenszel_statistics" title="Cochran–Mantel–Haenszel statistics">Cochran–Mantel–Haenszel statistics</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Multivariate_statistics" title="Multivariate statistics">Multivariate</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="General_linear_model" title="General linear model">Regression</a></li>
<li><a href="Multivariate_analysis_of_variance" title="Multivariate analysis of variance">Manova</a></li>
<li><a href="Principal_component_analysis" title="Principal component analysis">Principal components</a></li>
<li><a href="Canonical_correlation" title="Canonical correlation">Canonical correlation</a></li>
<li><a href="Linear_discriminant_analysis" title="Linear discriminant analysis">Discriminant analysis</a></li>
<li><a href="Cluster_analysis" title="Cluster analysis">Cluster analysis</a></li>
<li><a href="Statistical_classification" title="Statistical classification">Classification</a></li>
<li><a href="Structural_equation_modeling" title="Structural equation modeling">Structural equation model</a>
<ul><li><a href="Factor_analysis" title="Factor analysis">Factor analysis</a></li></ul></li>
<li><a href="Multivariate_distribution" class="mw-redirect" title="Multivariate distribution">Multivariate distributions</a>
<ul><li><a href="Elliptical_distribution" title="Elliptical distribution">Elliptical distributions</a>
<ul><li><a href="Multivariate_normal_distribution" title="Multivariate normal distribution">Normal</a></li></ul></li></ul></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Time_series" title="Time series">Time-series</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;">General</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Decomposition_of_time_series" title="Decomposition of time series">Decomposition</a></li>
<li><a href="Trend_estimation" class="mw-redirect" title="Trend estimation">Trend</a></li>
<li><a href="Stationary_process" title="Stationary process">Stationarity</a></li>
<li><a href="Seasonal_adjustment" title="Seasonal adjustment">Seasonal adjustment</a></li>
<li><a href="Exponential_smoothing" title="Exponential smoothing">Exponential smoothing</a></li>
<li><a href="Cointegration" title="Cointegration">Cointegration</a></li>
<li><a href="Structural_break" title="Structural break">Structural break</a></li>
<li><a href="Granger_causality" title="Granger causality">Granger causality</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;">Specific tests</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Dickey%E2%80%93Fuller_test" title="Dickey–Fuller test">Dickey–Fuller</a></li>
<li><a href="Johansen_test" title="Johansen test">Johansen</a></li>
<li><a href="Ljung%E2%80%93Box_test" title="Ljung–Box test">Q-statistic <span style="font-size: 85%;">(Ljung–Box)</span></a></li>
<li><a href="Durbin%E2%80%93Watson_statistic" title="Durbin–Watson statistic">Durbin–Watson</a></li>
<li><a href="Breusch%E2%80%93Godfrey_test" title="Breusch–Godfrey test">Breusch–Godfrey</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Time_domain" title="Time domain">Time domain</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Autocorrelation" title="Autocorrelation">Autocorrelation (ACF)</a>
<ul><li><a href="Partial_autocorrelation_function" title="Partial autocorrelation function">partial (PACF)</a></li></ul></li>
<li><a href="Cross-correlation" title="Cross-correlation">Cross-correlation (XCF)</a></li>
<li><a href="Autoregressive%E2%80%93moving-average_model" class="mw-redirect" title="Autoregressive–moving-average model">ARMA model</a></li>
<li><a href="Box%E2%80%93Jenkins_method" title="Box–Jenkins method">ARIMA model <span style="font-size: 85%;">(Box–Jenkins)</span></a></li>
<li><a href="Autoregressive_conditional_heteroskedasticity" title="Autoregressive conditional heteroskedasticity">Autoregressive conditional heteroskedasticity (ARCH)</a></li>
<li><a href="Vector_autoregression" title="Vector autoregression">Vector autoregression (VAR)</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Frequency_domain" title="Frequency domain">Frequency domain</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Spectral_density_estimation" title="Spectral density estimation">Spectral density estimation</a></li>
<li><a href="Fourier_analysis" title="Fourier analysis">Fourier analysis</a></li>
<li><a href="Least-squares_spectral_analysis" title="Least-squares spectral analysis">Least-squares spectral analysis</a></li>
<li><a href="Wavelet" title="Wavelet">Wavelet</a></li>
<li><a href="Whittle_likelihood" title="Whittle likelihood">Whittle likelihood</a></li></ul>
</div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Survival_analysis" title="Survival analysis">Survival</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Survival_function" title="Survival function">Survival function</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Kaplan%E2%80%93Meier_estimator" title="Kaplan–Meier estimator">Kaplan–Meier estimator (product limit)</a></li>
<li><a href="Proportional_hazards_model" title="Proportional hazards model">Proportional hazards models</a></li>
<li><a href="Accelerated_failure_time_model" title="Accelerated failure time model">Accelerated failure time (AFT) model</a></li>
<li><a href="First-hitting-time_model" title="First-hitting-time model">First hitting time</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;"><a href="Failure_rate" title="Failure rate">Hazard function</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Nelson%E2%80%93Aalen_estimator" title="Nelson–Aalen estimator">Nelson–Aalen estimator</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;font-weight:normal;">Test</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Log-rank_test" class="mw-redirect" title="Log-rank test">Log-rank test</a></li></ul>
</div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks mw-collapsible uncollapsed navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Applications654" style="font-size:114%;margin:0 4em"><a href="List_of_fields_of_application_of_statistics" title="List of fields of application of statistics">Applications</a></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Biostatistics" title="Biostatistics">Biostatistics</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Bioinformatics" title="Bioinformatics">Bioinformatics</a></li>
<li><a href="Clinical_trial" title="Clinical trial">Clinical trials</a>&nbsp;/ <a href="Clinical_study_design" title="Clinical study design">studies</a></li>
<li><a href="Epidemiology" title="Epidemiology">Epidemiology</a></li>
<li><a href="Medical_statistics" title="Medical statistics">Medical statistics</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Engineering_statistics" title="Engineering statistics">Engineering statistics</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Chemometrics" title="Chemometrics">Chemometrics</a></li>
<li><a href="Methods_engineering" title="Methods engineering">Methods engineering</a></li>
<li><a href="Probabilistic_design" title="Probabilistic design">Probabilistic design</a></li>
<li><a href="Statistical_process_control" title="Statistical process control">Process</a>&nbsp;/ <a href="Quality_control" title="Quality control">quality control</a></li>
<li><a href="Reliability_engineering" title="Reliability engineering">Reliability</a></li>
</ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Social_statistics" title="Social statistics">Social statistics</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Actuarial_science" title="Actuarial science">Actuarial science</a></li>
<li><a href="Census" title="Census">Census</a></li>
<li><a href="Crime_statistics" title="Crime statistics">Crime statistics</a></li>
<li><a href="Demographic_statistics" title="Demographic statistics">Demography</a></li>
<li><a href="Econometrics" title="Econometrics">Econometrics</a></li>
<li><a href="Jurimetrics" title="Jurimetrics">Jurimetrics</a></li>
<li><a href="National_accounts" title="National accounts">National accounts</a></li>
<li><a href="Official_statistics" title="Official statistics">Official statistics</a></li>
<li><a href="Population_statistics" class="mw-redirect" title="Population statistics">Population statistics</a></li>
<li><a href="Psychometrics" title="Psychometrics">Psychometrics</a></li></ul>
</div></td></tr><tr><th scope="row" class="navbox-group" style="width:12.5em"><a href="Spatial_analysis" title="Spatial analysis">Spatial statistics</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="padding:0"><div style="padding:0 0.25em">
<ul><li><a href="Cartography" title="Cartography">Cartography</a></li>
<li><a href="Environmental_statistics" title="Environmental statistics">Environmental statistics</a></li>
<li><a href="Geographic_information_system" title="Geographic information system">Geographic information system</a></li>
<li><a href="Geostatistics" title="Geostatistics">Geostatistics</a></li>
<li><a href="Kriging" title="Kriging">Kriging</a></li></ul>
</div></td></tr></tbody></table><div></div></td></tr></tbody></table><div></div></td></tr><tr><td class="navbox-abovebelow" colspan="2"><div>
<ul><li><span class="noviewer" typeof="mw:File"><span title="Category"></span></span><b>Category</b></li>
<li><b><span class="nowrap"><span class="skin-invert-image noviewer" typeof="mw:File"></span> </span><a href="Portal%3AMathematics" title="Portal:Mathematics">Mathematics portal</a></b></li>
<li><span class="noviewer" typeof="mw:File"><span title="Commons page"></span></span><b><a href="https://commons.wikimedia.org/wiki/Category:Statistics" class="extiw external" title="commons:Category:Statistics">Commons</a></b></li>
<li><span class="noviewer" typeof="mw:File"><span title="WikiProject"></span></span> <b>WikiProject</b></li></ul>
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