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id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">Mean opinion score</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. 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href="https://fr.wikipedia.org/wiki/Note_d%27opinion_moyenne" title="Note d'opinion moyenne – French" lang="fr" hreflang="fr" data-title="Note d'opinion moyenne" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/Mean_Opinion_Score" title="Mean Opinion Score – Italian" lang="it" hreflang="it" data-title="Mean Opinion Score" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/MOS_%C3%A9rt%C3%A9kel%C3%A9s" title="MOS értékelés – Hungarian" lang="hu" hreflang="hu" data-title="MOS értékelés" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/Mean_opinion_score" title="Mean opinion score – Dutch" lang="nl" hreflang="nl" data-title="Mean opinion score" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/%E5%B9%B3%E5%9D%87%E3%82%AA%E3%83%94%E3%83%8B%E3%82%AA%E3%83%B3%E8%A9%95%E7%82%B9" title="平均オピニオン評点 – Japanese" lang="ja" hreflang="ja" data-title="平均オピニオン評点" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/Mean_Opinion_Score" title="Mean Opinion Score – Polish" lang="pl" hreflang="pl" data-title="Mean Opinion Score" data-language-autonym="Polski" data-language-local-name="Polish" 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data-event-name="pinnable-header.vector-appearance.pin">move to sidebar</button> <button class="vector-pinnable-header-toggle-button vector-pinnable-header-unpin-button" data-event-name="pinnable-header.vector-appearance.unpin">hide</button> </div> </div> </div> </nav> </div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Measure of quality of a stimulus or system</div> <p><b>Mean opinion score</b> (<b>MOS</b>) is a measure used in the domain of <a href="/wiki/Quality_of_Experience" class="mw-redirect" title="Quality of Experience">Quality of Experience</a> and <a href="/wiki/Telecommunications_engineering" title="Telecommunications engineering">telecommunications engineering</a>, representing overall quality of a stimulus or system. It is the <a href="/wiki/Arithmetic_mean" title="Arithmetic mean">arithmetic mean</a> over all individual "values on a predefined scale that a subject assigns to his opinion of the performance of a system quality".<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> Such ratings are usually gathered in a <a href="/wiki/Subjective_video_quality" title="Subjective video quality">subjective quality evaluation test</a>, but they can also be algorithmically estimated. </p><p>MOS is a commonly used measure for video, audio, and audiovisual quality evaluation, but not restricted to those modalities. <a href="/wiki/ITU-T" title="ITU-T">ITU-T</a> has defined several ways of referring to a MOS in Recommendation <a rel="nofollow" class="external text" href="https://www.itu.int/rec/T-REC-P.800.1">ITU-T P.800.1</a>, depending on whether the score was obtained from audiovisual, conversational, listening, talking, or video quality tests. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="Rating_scales_and_mathematical_definition">Rating scales and mathematical definition</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mean_opinion_score&action=edit&section=1" title="Edit section: Rating scales and mathematical definition"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The MOS is expressed as a single rational number, typically in the range 1–5, where 1 is lowest perceived quality, and 5 is the highest perceived quality. Other MOS ranges are also possible, depending on the <a href="/wiki/Rating_scale" title="Rating scale">rating scale</a> that has been used in the underlying test. The <a href="/wiki/Absolute_Category_Rating" title="Absolute Category Rating">Absolute Category Rating</a> scale is very commonly used, which maps ratings between <i>Bad</i> and <i>Excellent</i> to numbers between 1 and 5, as seen in below table. </p> <table class="wikitable"> <tbody><tr> <th>Rating </th> <th>Label </th></tr> <tr> <td>5 </td> <td>Excellent </td></tr> <tr> <td>4 </td> <td>Good </td></tr> <tr> <td>3 </td> <td>Fair </td></tr> <tr> <td>2 </td> <td>Poor </td></tr> <tr> <td>1 </td> <td>Bad </td></tr></tbody></table> <p>Other standardized quality rating scales exist in <a href="/wiki/Category:ITU-T_recommendations" title="Category:ITU-T recommendations">ITU-T Recommendations</a> (such as <a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-P.800/en">ITU-T P.800</a> or <a rel="nofollow" class="external text" href="https://www.itu.int/rec/T-REC-P.910">ITU-T P.910</a>). For example, one could use a continuous scale ranging between 1–100. Which scale is used depends on the purpose of the test. In certain contexts there are no statistically significant differences between ratings for the same stimuli when they are obtained using different scales.<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><p>The MOS is calculated as the <a href="/wiki/Arithmetic_mean" title="Arithmetic mean">arithmetic mean</a> over single ratings performed by human subjects for a given stimulus in a <a href="/wiki/Subjective_video_quality" title="Subjective video quality">subjective quality evaluation test</a>. Thus: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle MOS={\frac {\sum _{n=1}^{N}{R_{n}}}{N}}}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>M</mi> <mi>O</mi> <mi>S</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <munderover> <mo>∑</mo> <mrow class="MJX-TeXAtom-ORD"> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>N</mi> </mrow> </munderover> <mrow class="MJX-TeXAtom-ORD"> <msub> <mi>R</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>n</mi> </mrow> </msub> </mrow> </mrow> <mi>N</mi> </mfrac> </mrow> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle MOS={\frac {\sum _{n=1}^{N}{R_{n}}}{N}}}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/e35e2a1af8060428649f1ca9c43e22b3d628f6d5" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.838ex; width:18.792ex; height:6.176ex;" alt="{\displaystyle MOS={\frac {\sum _{n=1}^{N}{R_{n}}}{N}}}"></span></dd></dl> <p>Where <span class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle R}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>R</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle R}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/4b0bfb3769bf24d80e15374dc37b0441e2616e33" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.764ex; height:2.176ex;" alt="{\displaystyle R}"></span></span> are the individual ratings for a given stimulus by <span class="nowrap"><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle N}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>N</mi> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle N}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/f5e3890c981ae85503089652feb48b191b57aae3" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:2.064ex; height:2.176ex;" alt="{\displaystyle N}"></span></span> subjects. </p> <div class="mw-heading mw-heading2"><h2 id="Properties_of_the_MOS">Properties of the MOS</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mean_opinion_score&action=edit&section=2" title="Edit section: Properties of the MOS"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The MOS is subject to certain mathematical properties and biases. In general, there is an ongoing debate on the usefulness of the MOS to quantify Quality of Experience in a single scalar value.<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> </p><p>When the MOS is acquired using a categorical rating scales, it is based on – similar to <a href="/wiki/Likert_scale" title="Likert scale">Likert scales</a> – an <a href="/wiki/Level_of_measurement#Ordinal_scale" title="Level of measurement">ordinal scale</a>. In this case, the ranking of the scale items is known, but their interval is not. Therefore, it is mathematically incorrect to calculate a mean over individual ratings in order to obtain the central tendency; the median should be used instead.<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> However, in practice and in the definition of MOS, it is considered acceptable to calculate the arithmetic mean. </p><p>It has been shown that for categorical rating scales (such as ACR), the individual items are not perceived equidistant by subjects. For example, there may be a larger "gap" between <i>Good</i> and <i>Fair</i> than there is between <i>Good</i> and <i>Excellent</i>. The perceived distance may also depend on the language into which the scale is translated.<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> However, there exist studies that could not prove a significant impact of scale translation on the obtained results.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p><p>Several other biases are present in the way MOS ratings are typically acquired.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> In addition to the above-mentioned issues with scales that are perceived non-linearly, there is a so-called "range-equalization bias": subjects, over the course of a subjective experiment, tend to give scores that span the entire rating scale. This makes it impossible to compare two different subjective tests if the range of presented quality differs. In other words, the MOS is never an absolute measure of quality, but only relative to the test in which it has been acquired. </p><p> For the above reasons – and due to several other contextual factors influencing the perceived quality in a subjective test – a MOS value should only be reported if the context in which the values have been collected in is known and reported as well. MOS values gathered from different contexts and test designs therefore should not be directly compared. Recommendation <a rel="nofollow" class="external text" href="https://www.itu.int/rec/T-REC-P.800.2">ITU-T P.800.2</a> prescribes how MOS values should be reported. Specifically, P.800.2 says:</p><blockquote><p>it is not meaningful to directly compare MOS values produced from separate experiments, unless those experiments were explicitly designed to be compared, and even then the data should be statistically analysed to ensure that such a comparison is valid.</p></blockquote> <div class="mw-heading mw-heading2"><h2 id="MOS_for_speech_and_audio_quality_estimation">MOS for speech and audio quality estimation</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mean_opinion_score&action=edit&section=3" title="Edit section: MOS for speech and audio quality estimation"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>MOS historically originates from <a href="/wiki/Subjectivity" class="mw-redirect" title="Subjectivity">subjective</a> measurements where listeners would sit in a "quiet room" and score a telephone call quality as they perceived it. This kind of test methodology had been in use in the telephony industry for decades and was standardized in Recommendation <a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-P.800">ITU-T P.800</a>. It specifies that "the talker should be seated in a quiet room with volume between 30 and 120 m³ and a reverberation time less than 500 ms (preferably in the range 200–300 ms). The room noise level must be below 30 dBA with no dominant peaks in the spectrum." Requirements for other modalities were similarly specified in later ITU-T Recommendations. </p> <div class="mw-heading mw-heading2"><h2 id="MOS_estimation_using_quality_models">MOS estimation using quality models</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mean_opinion_score&action=edit&section=4" title="Edit section: MOS estimation using quality models"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Obtaining MOS ratings may be time-consuming and expensive as it requires the recruitment of human assessors. For various use cases such as codec development or service quality monitoring purposes – where quality should be estimated repeatedly and automatically – MOS scores can also be predicted by <a href="/wiki/Video_quality#Objective_video_quality" title="Video quality">objective quality models</a>, which typically have been developed and trained using human MOS ratings. A question that arises from using such models is whether the MOS differences produced are noticeable to the users. For example, when rating images on a five point MOS scale, an image with a MOS equal to 5 is expected to be noticeably better in quality than one with a MOS equal to 1. Contrary to that, it is not evident whether an image with a MOS equal to 3.8 is noticeably better in quality than one with a MOS equal to 3.6. Research conducted on determining the smallest MOS difference that is perceptible to users for digital photographs showed that a MOS difference of approximately 0.46 is required in order for 75% of the users to be able to detect the higher quality image. <sup id="cite_ref-interpretMOS_8-0" class="reference"><a href="#cite_note-interpretMOS-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> Nevertheless, image quality expectation, and hence MOS, changes over time with the change of user expectations. As a result, minimum noticeable MOS differences determined using analytical methods such as in <sup id="cite_ref-interpretMOS_8-1" class="reference"><a href="#cite_note-interpretMOS-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> may change over time. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mean_opinion_score&action=edit&section=5" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/Absolute_Category_Rating" title="Absolute Category Rating">Absolute Category Rating</a></li> <li><a href="/wiki/Likert_scale" title="Likert scale">Likert scale</a></li> <li><a href="/wiki/MUSHRA" title="MUSHRA">MUSHRA</a> (Recommendation <a href="/wiki/ITU-R" title="ITU-R">ITU-R</a> BS.1534)</li> <li><a href="/wiki/Video_quality#Objective_video_quality" title="Video quality">Objective video quality</a></li> <li><a href="/wiki/Subjective_video_quality" title="Subjective video quality">Subjective video quality</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Mean_opinion_score&action=edit&section=6" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">ITU-T Rec. P.10/G.100 (2017) Vocabulary for performance, quality of service and quality of experience.</span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFHuynh-ThuGarciaSperanzaCorriveau2011" class="citation journal cs1">Huynh-Thu, Q.; Garcia, M. 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</div> </div> <div class="vector-sticky-header-end" aria-hidden="true"> <div class="vector-sticky-header-icons"> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only" id="ca-talk-sticky-header" tabindex="-1" data-event-name="talk-sticky-header"><span class="vector-icon mw-ui-icon-speechBubbles mw-ui-icon-wikimedia-speechBubbles"></span> <span></span> </a> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only" id="ca-subject-sticky-header" tabindex="-1" data-event-name="subject-sticky-header"><span class="vector-icon mw-ui-icon-article mw-ui-icon-wikimedia-article"></span> <span></span> </a> <a href="#" class="cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only" id="ca-history-sticky-header" tabindex="-1" data-event-name="history-sticky-header"><span 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