Editing Intelligence quotient (section)

===Precursors to IQ testing===
Historically, even before IQ tests were devised, there were attempts to classify people into [[Human intelligence|intelligence]] categories by observing their behavior in daily life.<ref name="TermanOldClasses" /><ref name="WechslerOldClasses" /> Those other forms of behavioral observation are still important for validating classifications based primarily on IQ test scores. Both intelligence classification by observation of behavior outside the testing room and classification by IQ testing depend on the definition of "intelligence" used in a particular case and on the [[Reliability (psychometrics)|reliability]] and error of estimation in the classification procedure.

The English statistician [[Francis Galton]] (1822–1911) made the first attempt at creating a standardized test for rating a person's intelligence. A pioneer of [[psychometrics]] and the application of statistical methods to the study of human diversity and the study of inheritance of human traits, he believed that intelligence was largely a product of heredity (by which he did not mean [[History of genetics#Post-Mendel, pre-re-discovery|genes]], although he did develop several [[Mendelian inheritance|pre-Mendelian]] theories of particulate inheritance).<ref>{{cite journal |last1=Bulmer |first1=M |year=1999 |title=The development of Francis Galton's ideas on the mechanism of heredity |journal=Journal of the History of Biology |volume=32 |issue=3 |pages=263–292 | doi = 10.1023/a:1004608217247 |pmid=11624207 |s2cid=10451997}}</ref><ref>{{cite journal |last1=Cowan |first1=R. S. |year=1972 |title=Francis Galton's contribution to genetics |journal=Journal of the History of Biology |volume=5 |issue=2 |pages=389–412 |doi=10.1007/bf00346665|pmid=11610126 |s2cid=30206332}}</ref><ref>{{cite journal |last1=Burbridge |first1=D |year=2001 |title=Francis Galton on twins, heredity and social class |journal=British Journal for the History of Science |volume=34 |issue=3 |pages=323–340 |doi=10.1017/s0007087401004332|pmid=11700679}}</ref> He hypothesized that there should exist a correlation between intelligence and other observable traits such as [[reflex]]es, muscle grip, and [[Craniometry#Bertillon, Galton and criminology|head size]].<ref>{{cite journal |last1=Fancher |first1=R. E. |year=1983 |title=Biographical origins of Francis Galton's psychology |journal=Isis |volume=74 |issue=2 |pages=227–233 |doi=10.1086/353245|pmid=6347965|s2cid=40565053 }}</ref> He set up the first mental testing center in the world in 1882 and he published "Inquiries into Human Faculty and Its Development" in 1883, in which he set out his theories. After gathering data on a variety of physical variables, he was unable to show any such correlation, and he eventually abandoned this research.<ref name="Kaufman2009p21" /><ref>{{cite journal |last1=Gillham |first1=Nicholas W. |title=Sir Francis Galton and the birth of eugenics |journal=Annual Review of Genetics |volume=35 |issue=1 |pages=83–101 |year=2001 |pmid=11700278 |doi=10.1146/annurev.genet.35.102401.090055}}</ref>
[[File:Alfred Binet.jpg|thumb|upright|Psychologist [[Alfred Binet]], co-developer of the [[Stanford–Binet Intelligence Scales|Stanford–Binet test]]]]
French psychologist [[Alfred Binet]] and psychiatrist [[Théodore Simon]], had more success in 1905, when they published the [[Binet-Simon Intelligence Test|Binet–Simon Intelligence test]], which focused on verbal abilities.<ref name=":15" /> It was intended to identify "mental retardation" in school children,<ref name=Kaufman2009/> but in specific contradistinction to claims made by psychiatrists that these children were "sick" (not "slow") and should therefore be removed from school and cared for in asylums.<ref name=":15">{{cite journal |last1=Nicolas |first1=S. |last2=Andrieu |first2=B. |last3=Croizet |first3=J.-C. |last4=Sanitioso |first4=R. B. |last5=Burman |first5=J. T. |year=2013 |title=Sick? Or slow? On the origins of intelligence as a psychological object |journal=Intelligence |volume=41 |issue=5 |pages=699–711 |doi=10.1016/j.intell.2013.08.006 |doi-access=free}} (This is an [[open access]] article, made freely available by [[Elsevier]].)</ref> The score on the Binet–Simon scale would reveal the child's [[mental age]]. For example, a six-year-old child who passed all the tasks usually passed by six-year-olds—but nothing beyond—would have a mental age that matched his chronological age, 6.0. (Fancher, 1985). Binet and Simon thought that intelligence was multifaceted, but came under the control of practical judgment.

In Binet and Simon's view, there were limitations with the scale and they stressed what they saw as the remarkable diversity of intelligence and the subsequent need to study it using qualitative, as opposed to quantitative, measures (White, 2000). American psychologist [[Henry H. Goddard]] published a translation of it in 1910. American psychologist [[Lewis Terman]] at [[Stanford University]] revised the Binet–Simon scale, which resulted in the [[Stanford–Binet Intelligence Scales|Stanford revision of the Binet-Simon Intelligence Scale]] (1916). It became the most popular test in the United States for decades.<ref name=Kaufman2009/>{{sfn|Terman et al.|1915}}<ref>{{cite journal |last1=Wallin |first1=J. E. W. |title=The new clinical psychology and the psycho-clinicist |journal=Journal of Educational Psychology |volume=2 |issue=3 |pages=121–32 |year=1911 |doi=10.1037/h0075544 |url=https://zenodo.org/record/1429171}}</ref><ref>{{cite journal |last1=Richardson |first1=John T. E. |title=Howard Andrew Knox and the origins of performance testing on Ellis Island, 1912-1916 |journal=History of Psychology |volume=6 |issue=2 |pages=143–70 |year=2003 |pmid=12822554 |doi=10.1037/1093-4510.6.2.143}}</ref>

The abbreviation "IQ" was coined by the [[psychologist]] [[William Stern (psychologist)|William Stern]] for the [[German language|German]] term {{lang|de|Intelligenzquotient}}, his term for a scoring method for [[intelligence]] tests at [[University of Wrocław|University of Breslau]] he advocated in a 1912 book.{{sfn|Stern|1914|pp=70–84 (1914 English translation); pp. 48–58 (1912 original German edition)}}