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Monday, January 31, 2011

IQ and the birth of psychometrics

IQ and the birth of psychometrics
Later, Binet used the idea of the average age at which a task was mastered to derive a child’s mental age – a radically new concept. Mental age (MA) is equivalent to the chronological age (CA) for which any test score would represent average performance. So a child scoring better than the average child of his age would have a higher MA than CA, and a child scoring lower than average would have a lower MA than CA. It took one short step, by Stern (1914), to derive an index of differences in intelligence within ages. The resulting intelligence quotient, or IQ, was calculated using the classical formula, IQ = MA/CA × 100. The calculation of IQ gave birth to two ideas:
1. individual differences in intelligence can be expressed by a single score (note that this notion of a single score actually presumes the existence of g); and
2. a range of measures of performance on different kinds of knowledge, judgement and reasoning tasks (as evaluated by tests such as Binet’s) can be taken together to contribute to our understanding of intelligence.

Psychometrics or the measurement of human abilities (later extended to other attributes) was therefore born. Stern’s formulation helped to drive a wedge between the two different approaches to studying intelligence – the individual differences method (concerned with IQ differences among peers) and the developmental method (concerned with changes in MA with CA). And this wedge finally culminated in these different research approaches being split apart through the work of Jean Piaget.

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