Intelligence at adulthood: A twenty-five year follow-up.

Abstract

This paper reports findings from 111 Ss tested with the Stanford-Binet (S-B) at preschool and adolescence who were administered the S-B and WAIS at adulthood. Correlations of preschool IQs with adult S-B and full WAIS IQs are .59 and .64; of adolescent IQs with adult IQs, .85 and .80. Mean S-B IQ increase from adolescence to adulthood is 11 points, indicating that mental growth continues beyond 16 years. Males show more IQ gain after adolescence than do females (p < .01). Girls with high IQs increase least. Analysis of increases in percent passing S-B items shows more growth after adolescence in abstract reasoning and vocabulary than in rote memory and practical reasoning. Preschool verbal and memory items are better predictors than nonverbal items of both verbal and performance adult IQs. Pattern of individual differences in relative amounts of these abilities shows some stability over 25 years.

Changes in Iq, Environmental and Individual Factors: A Follow‐up Study of Educable Mentally Retarded Children

“…A similar development was also observed for the three hearing impaired persons included in this study. No correlations were observed between the men's I.Q.s as children and I.Q.s obtained at adult age, while significant correlations have been reported in follow-up studies of non-retarded persons (Bradway and Thompson, 1962;Hindley, 1965).…”

Policy Implications of the IQ Controversy

“…Compared with other behavioral traits, however, IQ scores become remarkably stable after about age six. Brodway and Thompson (1962) reported test-retest correlations of intelligence scores of .85 over a 15-year period from adolescence to adulthood, of .65 over a 10-year period from preschool to adolescence, and of .59 over the 25-year period from preschool to adulthood. In the Fels longitudinal study of 89 children, Kagan and Moss (1962) found a correlation of .54 for intelligence over a seven-year period beginning at ages 3 to 6, and a correlation of .78 over a five-year period beginning at ages 6 to 10. gence have their major impact early in life, and that later environmental influences do little to disturb the early-established rank order of individuals.…”

The temporal stability of individually tested intelligence

“…Subject sex and specific instrument were not found to have a significant effect on reliability. A summary table provides expected reliability coefficients, standard error, and percent of persons with IQ change in excess of 15 points, tabulated for combinations of each of the two predictors.Reviews of the temporal stability of individually administered intelligence tests have appeared sporadically over the last 50 years or so (Bradway & Thompson, 1962;Brown, 1933;Zimmerman & Woo-Sam, 1972). What is lacking is an integrative review of studies across instruments; at least, if there is one, we failed to find it.…”