Intelligence and its measurement
Intelligence testing began as a practical tool: Alfred Binet and Théodore Simon built a scale in 1905 to identify French schoolchildren who needed extra help, by comparing a child's performance against what was typical for their age. American psychologists turned that scale into the IQ score, standardised so that the population average is 100, and used it far beyond Binet's intended purpose, including in immigration and eugenic arguments he would not have endorsed. Scores on different mental tests correlate with each other, and the shared variance is labelled g, or general intelligence; what g actually is, and whether one number can represent a person's mind, remain live disputes. Test scores predict school and job performance at a group level well above chance, and predict any single individual far less well.
Why it matters
It is the clearest case in psychology of a measurement outrunning the theory behind it, and of a tool built for one purpose being used for another.
Also written: IQ, intelligence quotient, g factor, psychometrics
Where it comes up
Read about Intelligence and its measurement on Wikipedia
Sources
- Intelligence quotient Wikipedia
- New Methods for the Diagnosis of the Intellectual Level of Subnormals Classics in the History of Psychology, York UniversityBinet and Simon's own 1905 paper, which states the narrow purpose the scale was built for.
- Psychometrics Wikipedia
