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.