{"id":7814,"date":"2019-05-22T16:00:56","date_gmt":"2019-05-22T16:00:56","guid":{"rendered":"http:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/effect_size\/"},"modified":"2019-05-22T16:00:56","modified_gmt":"2019-05-22T16:00:56","slug":"effect_size","status":"publish","type":"post","link":"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/effect_size\/","title":{"rendered":"Effect size"},"content":{"rendered":"<p>A family of statistical measures that provides an indication of the magnitude of a treatment effect. &nbsp;In contrast to significance tests, they are independent of sample size, and therefore generally used in meta-analyses. &nbsp;Broadly speaking, effect size boils down to two measurements:&nbsp;the standardised difference between two means of two independent groups, and the effect size correlation (i.e., the correlation between the independent variable and scores on the dependent variable). &nbsp;For the first measure, one can either use Cohen&#8217;s <span class=\"\" style=\"font-style: italic;\">d<\/span> (difference between the means divided by the standard deviation of either group) or <a href=\"http:\/\/l-hedges@northwestern.edu\/\" data-editable-link=\"http:\/\/l-hedges@northwestern.edu&amp;target=_self\" target=\"_self\" rel=\"noopener noreferrer\">Hedges <\/a><span class=\"\" style=\"font-style: italic;\">g<\/span> (difference between the means divided by the square root of the mean square error derived from an ANOVA). &nbsp;For the second, it amounts to a point-biserial correlation between a dichotomous independent variable and a continuously scaled dependent variable. &nbsp;While bearing in mind the degree of subjectivity involved, effect sizes of 0.8 and greater are considered to be &#8216;large&#8217;, with those between 0.3 and 0.5 and between 0.0 and .0.2 being classified as &#8216;medium&#8217; and &#8216;small&#8217;, respectively. Thus, for example, an effect size of 0.8 means that the score of an &#8216;average&#8217; individual in the experimental group exceeds the scores of 79% of the control group. &nbsp;There is some debate about the best way to compute effect sizes for dependent or repeated measures. &nbsp;In such cases, it is recommended to use the original standard deviations rather than the paired t-test value or the within-subject F value.&nbsp;<\/p>\n<p>See <a href=\"analysis_of_variance_-anova-\">Analysis of variance (ANOVA)<\/a>, <a href=\"error_term\">Error term<\/a>, <a href=\"influence_efficacy\">Influence efficacy<\/a>, <a href=\"meta-analysis\">Meta-analysis<\/a>, <a href=\"precision\">Precision<\/a>, <a href=\"statistical_power\">Statistical power<\/a><\/p>\n<p><\/p>\n<p><\/p>\n<p><\/body><\/html><\/p>\n","protected":false},"excerpt":{"rendered":"<p>A family of statistical measures that provides an indication of the magnitude of a treatment effect. &nbsp;In contrast to significance tests, they are independent of sample size, and therefore generally used in meta-analyses. &nbsp;Broadly speaking, effect size boils down to two measurements:&nbsp;the standardised difference between two means of two independent groups, and the effect size &hellip; <\/p>\n<p class=\"link-more\"><a href=\"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/effect_size\/\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;Effect size&#8221;<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[2],"class_list":["post-7814","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-glossary","entry"],"_links":{"self":[{"href":"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/wp-json\/wp\/v2\/posts\/7814","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/wp-json\/wp\/v2\/comments?post=7814"}],"version-history":[{"count":0,"href":"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/wp-json\/wp\/v2\/posts\/7814\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/wp-json\/wp\/v2\/media?parent=7814"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/wp-json\/wp\/v2\/categories?post=7814"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.lancaster.ac.uk\/fas\/psych\/glossary\/wp-json\/wp\/v2\/tags?post=7814"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}