Editing Intelligence quotient (section)

===Flynn effect===
{{Main|Flynn effect}}

Since the early 20th century, raw scores on IQ tests have increased in most parts of the world.<ref name="Neisser1998">{{Cite book|title=The Rising Curve: Long-Term Gains in IQ and Related Measures |editor-last=Neisser |editor-first=Ulric |display-authors=8 |author1=Ulric Neisser |author2=James R. Flynn |author3=Carmi Schooler |author4=Patricia M. Greenfield |author5=Wendy M. Williams |author6=Marian Sigman |author7=Shannon E. Whaley |author8=Reynaldo Martorell |author9=Richard Lynn |author10=Robert M. Hauser |author11=David W. Grissmer |author12=Stephanie Williamson |author13=Sheila Nataraj Kirby |author14=Mark Berends |author15=Stephen J. Ceci |author16=Tina B. Rosenblum |author17=Matthew Kumpf |author18=Min-Hsiung Huang |author19=Irwin D. Waldman |author20=Samuel H. Preston |author21=John C. Loehlin |year=1998 |publisher=American Psychological Association |location=Washington, DC |isbn=978-1-55798-503-3 |series=APA Science Volume Series |url=https://archive.org/details/risingcurvelongt00neis}}{{Page needed|date=January 2011}}</ref>{{sfn|Mackintosh|1998|p={{Page needed|date=January 2011}}}}{{sfn|Flynn|2009|p={{Page needed|date=January 2011}}}} When a new version of an IQ test is normed, the standard scoring is set so performance at the population median results in a score of IQ 100. The phenomenon of rising raw score performance means if test-takers are scored by a constant standard scoring rule, IQ test scores have been rising at an average rate of around three IQ points per decade. This phenomenon was named the Flynn effect in the book ''[[The Bell Curve]]'' after [[Jim Flynn (academic)|James R. Flynn]], the author who did the most to bring this phenomenon to the attention of psychologists.<ref name="Flynn1984">{{cite journal |last1=Flynn |first1=James R. |title=The mean IQ of Americans: Massive gains 1932 to 1978. |journal=Psychological Bulletin |volume=95 |issue=1 |pages=29–51 |year=1984 |doi=10.1037/0033-2909.95.1.29 |s2cid=51999517}}</ref><ref name="Flynn1987">{{cite journal |last1=Flynn |pages=171–91 |first1=James R. |issue=2 |volume=101 |year=1987 |title=Massive IQ gains in 14 nations: What IQ tests really measure. |doi=10.1037/0033-2909.101.2.171 |journal=Psychological Bulletin}}</ref>

Researchers have been exploring the issue of whether the Flynn effect is equally strong on performance of all kinds of IQ test items, whether the effect may have ended in some developed nations, whether there are social subgroup differences in the effect, and what possible causes of the effect might be.<ref>{{Cite book |last1=Zhou |first1=Xiaobin |last2=Grégoire |first2=Jacques |last3=Zhu |first3=Jianjin |title=WAIS-IV Clinical Use and Interpretation: Scientist-Practitioner Perspectives |editor1-last=Weiss |editor1-first=Lawrence G. |editor2-last=Saklofske |editor2-first=Donald H. |editor3-last=Coalson |editor3-first=Diane |editor4-last=Raiford |editor4-first=Susan |chapter=The Flynn Effect and the Wechsler Scales |year=2010 |publisher=Academic Press |location=Amsterdam |series=Practical Resources for the Mental Health Professional |isbn=978-0-12-375035-8}}{{Page needed|date=January 2011}}</ref> A 2011 textbook, ''IQ and Human Intelligence'', by [[Nicholas Mackintosh|N. J. Mackintosh]], noted the Flynn effect demolishes the fears that IQ would be decreased. He also asks whether it represents a real increase in intelligence beyond IQ scores.{{sfn|Mackintosh|2011|pp=25–27}} A 2011 psychology textbook, lead authored by Harvard Psychologist Professor [[Daniel Schacter]], noted that humans' inherited intelligence could be [[dysgenics|going down]] while acquired intelligence goes up.<ref>{{cite book |first1=Daniel L. |last1=Schacter |first2=Daniel T. |last2=Gilbert |first3=Daniel M. |last3=Wegner |title=Psychology|date=2011 |publisher=Palgrave Macmillan |location=Basingstoke |isbn=978-0230579835 |page=384}}</ref>

Research has suggested that the Flynn effect has slowed or reversed course in some Western countries beginning in the late 20th century. The phenomenon has been termed the ''negative Flynn effect''.<ref name=":4">{{Cite journal|last1=Bratsberg|first1=Bernt|last2=Rogeberg|first2=Ole|date=26 June 2018|title=Flynn effect and its reversal are both environmentally caused |journal=Proceedings of the National Academy of Sciences|volume=115 |issue=26|pages=6674–6678|doi=10.1073/pnas.1718793115|pmid=29891660|pmc=6042097|bibcode=2018PNAS..115.6674B |doi-access=free}}</ref> A study of Norwegian military conscripts' test records found that IQ scores have been falling for generations born after the year 1975, and that the underlying cause of both initial increasing and subsequent falling trends appears to be environmental rather than genetic.<ref name=":4" />