The stability of IQ in people with low intellectual ability: an analysis of the literature.
A meta-analysis of the stability of low IQ (IQ < 80) was performed on IQ tests that have been commonly used--tests that were derived by D. Wechsler (1949, 1955, 1974, 1981, 1991, 1997) and those based on the Binet scales (L. M. Terman, 1960; L. M. Terman & Merrill, 1972). Weighted-mean stability coefficients of .77 and .78 were found for Verbal IQ (V IQ) and Performance IQ (P IQ) on the Wechsler tests and .82 for Full-Scale IQ (FS IQ) on both Wechsler and Binet tests, for a mean test-retest interval of 2.8 years. Although the majority of FS IQs changed by less than 6 points, 14% changed by 10 points or more. The author suggests that the results of IQ assessment should be treated with more caution than previously thought.
Whitaker
Simon
S
Learning Disability Research Unit, University of Huddersfield, Queensgate, Huddersfield, United Kingdom. s.whitaker@hud.ac.uk
D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008607:Intellectual Disability / Q000175:diagnosis*; D007360:Intelligence; D008297:Male; D011594:Psychometrics; D014888:Wechsler Scales / Q000706:statistics & numerical data