Editing Intelligence quotient (section)

===Reliability===
{|class="wikitable sortable" style="font-size:small; float:right; text-align:center; margin:0 0 0.5em 1em" summary="Sortable table showing actual I.Q. scores of twelve students on three different I.Q. tests, with students identified by pseudonyms in cited data source."
|+ IQ scores can differ to some degree for the same person on different IQ tests, so a person does not always belong to the same IQ score range each time the person is tested. (IQ score table data and pupil pseudonyms adapted from description of KABC-II norming study cited in {{harvp|Kaufman|2009}}.<ref name="Kaufman2009Fig5.1" /><ref name="KaufmanSB2013Fig3.1" />)
|-
! class="unsortable" |Pupil!!KABC-II!!WISC-III!!WJ-III
|-
|A||90||95||111
|-
|B||125||110||105
|-
|C||100||93||101
|-
|D||116||127||118
|-
|E||93||105||93
|-
|F||106||105||105
|-
|G||95||100||90
|-
|H||112||113||103
|-
|I||104||96||97
|-
|J||101||99||86
|-
|K||81||78||75
|-
|L||116||124||102
|}

Psychometricians generally regard IQ tests as having high [[Reliability (psychometrics)|statistical reliability]].{{sfn|Neisser et al.|1995}}<ref name="Mackintosh2011p169">{{Harvnb |Mackintosh|2011|page=169}} "after the age of 8–10, IQ scores remain relatively stable: the correlation between IQ scores from age 8 to 18 and IQ at age 40 is over 0.70."</ref> Reliability represents the measurement consistency of a test.<ref name="Weiten">{{cite book|vauthors= Weiten W|title=Psychology: Themes and Variations |publisher=[[Cengage Learning]]|year=2016|page=281|isbn=978-1305856127 |url=https://books.google.com/books?id=ALkaCgAAQBAJ&pg=PT331}}</ref> A reliable test produces similar scores upon repetition.<ref name="Weiten"/> On aggregate, IQ tests exhibit high reliability, although test-takers may have varying scores when taking the same test on differing occasions, and may have varying scores when taking different IQ tests at the same age. Like all statistical quantities, any particular estimate of IQ has an associated standard error that measures uncertainty about the estimate. For modern tests, the confidence interval can be approximately 10 points and reported [[standard error of measurement]] can be as low as about three points.<ref>{{cite web |title=WISC-V Interpretive Report Sample |website=Pearson |url=https://images.pearsonclinical.com/images/assets/wisc-v/WISC-VInterpretiveReportSample-1.pdf |access-date=29 September 2020 |pages=18 |archive-date=22 April 2022 |archive-url=https://web.archive.org/web/20220422190842/https://images.pearsonclinical.com/images/assets/wisc-v/WISC-VInterpretiveReportSample-1.pdf |url-status=dead }}</ref> Reported standard error may be an underestimate, as it does not account for all sources of error.<ref>{{cite book |last1=Kaufman |first1=Alan S. |last2=Raiford |first2=Susan Engi |last3=Coalson |first3=Diane L. |year=2016 |title=Intelligent testing with the WISC-V |publisher=Wiley |location=Hoboken, NJ |isbn=978-1-118-58923-6 |pages=683–702 |quote=Reliability estimates in Table 4.1 and standard errors of measurement in Table 4.4 should be considered best-case estimates because they do not consider other major sources of error, such as transient error, administration error, or scoring error (Hanna, Bradley, & Holen, 1981), which influence test scores in clinical assessments. Another factor that must be considered is the extent to which subtest scores reflect portions of true score variance due to a hierarchical general intelligence factor and variance due to specific group factors because these sources of true score variance are conflated.}}</ref>

Outside influences such as low motivation or high anxiety can occasionally lower a person's IQ test score.<ref name="Weiten" /> For individuals with very low scores, the 95% confidence interval may be greater than 40 points, potentially complicating the accuracy of diagnoses of intellectual disability.<ref>{{cite journal |last1=Whitaker |first1=Simon |title=Error in the estimation of intellectual ability in the low range using the WISC-IV and WAIS-III |journal=Personality and Individual Differences |date=April 2010 |volume=48 |issue=5 |pages=517–521 |url=https://www.researchgate.net/publication/222824571 |access-date=22 January 2020 |doi=10.1016/j.paid.2009.11.017}}</ref> By the same token, high IQ scores are also significantly less reliable than those near to the population median.<ref>{{harvnb|Lohman|Foley Nicpon|2012|p={{page needed|date=October 2020}}}}. "The concerns associated with SEMs [standard errors of measurement] are actually substantially worse for scores at the extremes of the distribution, especially when scores approach the maximum possible on a test ... when students answer most of the items correctly. In these cases, errors of measurement for scale scores will increase substantially at the extremes of the distribution. Commonly the SEM is from two to four times larger for very high scores than for scores near the mean (Lord, 1980)."</ref> Reports of IQ scores much higher than 160 are considered dubious.<ref>{{harvnb|Urbina|2011|p=20}} "[Curve-fitting] is just one of the reasons to be suspicious of reported IQ scores much higher than 160"</ref>