The stability of IQ in people with low intellectual ability: an analysis of the literature

Intellect Dev Disabil. 2008 Apr;46(2):120-8. doi: 10.1352/0047-6765(2008)46[120:TSOIIP]2.0.CO;2.


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.

MeSH terms

  • Adolescent
  • Adult
  • Child
  • Female
  • Follow-Up Studies
  • Humans
  • Intellectual Disability / diagnosis*
  • Intelligence*
  • Male
  • Psychometrics
  • Wechsler Scales / statistics & numerical data