Innovated in a 1912 book by psychologist William Stern, Intelligence Quotient (IQ) is a derived cumulative score of several standardized tests meant to assess general human intelligence. IQ scores often play pivotal roles in intellectual disability assessments, job-applicant evaluations, and educational placement, though test subjects can and often do improve standardized test scores without actually improving cognitive memory, attention or speed capacities.
Testers define a norming sample’s median raw score as IQ 100 and each standard deviation (SD) up or down is defined as 15 IQ points in either direction. On average, only around 5 percent of the tested population scores over IQ 125, whereas approximately two-thirds rate between IQ 85 and 115. Researchers frequently associate these scores with a variety of factors, including mortality and morbidity, biological parental IQ and parental social status, although debate remains strong after nearly a century of research regarding the true significance of inheritance mechanisms and heritability estimates respectively.
Research has validated IQ scores strong job performance and income predictors and significant variables in psychometric intelligence-based population studies. Researchers have found that IQ scores have steadily risen among many populations since the early 20th century at a rate scaling to 3 IQ points per decade, a phenomenon named the Flynn Effect after The Bell Curve author and pioneering researcher James R. Flynn. Many present-day researchers still debate whether IQ tests of all kinds are equally affected in their performances by the Flynn Effect, as well as whether some developed nations may have surpassed the effect entirely, whether it manifests differently among various social subgroups, and may cause it. The 1998 textbook IQ and Human Intelligence points out the dysgenic trends researchers mistakenly believed gradually reduced the general population’s overall intelligence prior to the publishing of Flynn’s major papers and the early belief that IQ developed with no significant environmental influence.
Terms related to IQ
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- Definition of IQ