Editing Flynn effect (section)

==Possible end of progression==
[[File:Sundet et al 2004 fig 3.svg|thumb|right|Mean standing height and mean GA (both in z scores units+5) by year of testing, from Sundet et al. 2004 (figure 3)]]
Jon Martin Sundet and colleagues (2004) examined scores on intelligence tests given to [[Norway|Norwegian]] [[Norwegian Armed Forces#Conscription|conscripts]] between the 1950s and 2002. They found that the increase of scores of general intelligence stopped after the mid-1990s and declined in numerical reasoning sub-tests.<ref name="doi10.1016/j.intell.2004.06.004"/>

Teasdale and Owen (2005) examined the results of IQ tests given to [[Denmark|Danish]] male conscripts. Between 1959 and 1979 the gains were 3 points per decade. Between 1979 and 1989 the increase approached 2 IQ points. Between 1989 and 1998 the gain was about 1.3 points. Between 1998 and 2004 IQ declined by about the same amount as it gained between 1989 and 1998. They speculate that "a contributing factor in this recent fall could be a simultaneous decline in proportions of students entering 3-year advanced-level school programs for 16–18-year-olds."<ref name="Teasdale2005">{{cite journal|last1=Teasdale|first1=Thomas W.|last2=Owen|first2=David R.|year=2005|title=A long-term rise and recent decline in intelligence test performance: The Flynn Effect in reverse|journal=Personality and Individual Differences|volume=39|issue=4|pages=837–43|doi=10.1016/j.paid.2005.01.029}}</ref> The same authors in a more comprehensive 2008 study, again on Danish male conscripts, found that there was a 1.5-point increase between 1988 and 1998, but a 1.5-point decrease between 1998 and 2003/2004.<ref name = "reversal">{{cite journal |doi=10.1016/j.intell.2007.01.007 |vauthors=Teasdale TW, Owen DR |title=Secular declines in cognitive test scores: A reversal of the Flynn Effect |journal=Intelligence |volume=36 |issue=2 |pages=121–26 |year=2008 |url=http://www.iapsych.com/iqmr/fe/LinkedDocuments/teasdale2008.pdf |access-date=April 18, 2010 |archive-date=October 15, 2012 |archive-url=https://web.archive.org/web/20121015184832/http://www.iapsych.com/iqmr/fe/LinkedDocuments/teasdale2008.pdf |url-status=live }}</ref>

In Australia, the IQ of 6–12-year-olds (as measured by [[Raven's Progressive Matrices|colored progressive matrices]]) has shown no increase from 1975 to 2003.<ref>{{cite journal | last1=Cotton | first1= S.M.| last2= Kiely| first2= P.M.|last3= Crewther|first3= D.P.|last4= Thomson|first4= B.|last5= Laycock|first5= R.|last6= Crewther|first6= S.G. |year=2005|title= A normative and reliability study for the Raven's Colored Progressive Matrices for primary school aged children in Australia|journal= Personality and Individual Differences|volume= 39| issue= 3|pages= 647–60| doi = 10.1016/j.paid.2005.02.015}}</ref>

In the United Kingdom, a study by Flynn (2009) himself found that tests carried out in 1980 and again in 2008 show that the IQ score of an average 14-year-old dropped by more than two points over the period. For the upper half of the results, the performance was even worse. Average IQ scores declined by six points. However, children aged between five and 10 saw their IQs increase by up to half a point a year over the three decades. Flynn argues that the abnormal drop in British teenage IQ could be due to youth culture having "stagnated" or even dumbed down.<ref name="requiem">{{Cite journal| doi = 10.1016/j.ehb.2009.01.009 | pmid =   19251490| last1 = Flynn | first1 = J.R. | title = Requiem for nutrition as the cause of IQ gains: Raven's gains in Britain 1938–2008 | journal = Economics & Human Biology | volume = 7 | issue = 1 | pages = 18–27 | year = 2009 }}</ref>

Bratsberg & Rogeberg (2018) present evidence that the Flynn effect in Norway has reversed between the years 1962–1991, and that both the original rise in mean IQ scores and their subsequent decline within this period can be observed within families consisting of native-born parents and their children, indicating that environmental factors were the likely cause for these changes. Because IQ data was only available for male Norwegians, who were subject to military conscription, years of schooling were used as an approximation for female IQ to support this conclusion.<ref name="pnas2018" />

One possible explanation of a worldwide decline in intelligence is an increase in air pollution; coal burning emits mercury, and intelligence has continued to climb in areas, like the southern United States, where coal burning has declined.<ref>{{cite journal|first1=Ivica|last1=Pesovski|first2=Andrea|last2=Kulakov|first3=Vladimir|last3=Trajkovikj|title=Differences in cognitive ability assessment results between Millennial and Generation Z cohorts|url=https://repository.ukim.mk/handle/20.500.12188/25674|date=2022|journal=The 19th International Conference on Informatics and Information Technologies – CIIT 2022}}</ref><ref>{{cite journal|first1=Bernt|last1=Bratsberg|first2=Ole|last2=Rogeberg|title=Flynn effect and its reversal are both environmentally caused|journal=Proceedings of the National Academy of Sciences|date=26 June 2018|issn=0027-8424|pages=6674–6678|volume=115|issue=26|pmid=29891660|pmc=6042097|doi=10.1073/pnas.1718793115|doi-access=free |bibcode=2018PNAS..115.6674B }}</ref>

Winter et al. (2024) when comparing two [[Wechsler Adult Intelligence Scale|WAIS-5]] validity studies found a reduced Flynn effect of an increase of 1.2 IQ points per decade rather than the expected 3 IQ point increase per decade. The authors identified various novel factors including [[social media]] dependency and the [[Impact of COVID-19 on neurological, psychological and other mental health outcomes|COVID-19 pandemic]] which may have contributed to a reduced Flynn effect.<ref>{{Cite journal |last1=Winter |first1=Emily L. |last2=Trudel |first2=Sierra M. |last3=Kaufman |first3=Alan S. |date=2024-11-15 |title=Wait, Where's the Flynn Effect on the WAIS-5? |journal=Journal of Intelligence |language=en |volume=12 |issue=11 |pages=118 |doi=10.3390/jintelligence12110118 |doi-access=free |issn=2079-3200|pmc=11595985 }}</ref>