Intelligence was assessed at ages 11, 17, and 24 using abbreviated versions of the Wechsler Intelligence Scale for Children–Revised (WISC-R31) and the Wechsler Adult Intelligence Scale–Revised (WAIS-R32). The abbreviated versions consist of 2 verbal (Vocabulary and Information) and 2 performance (Block Design and Picture Arrangement) subtests. These subtests were selected for their high correlation (.90) with total IQ. Achievement was assessed at various ages using the Wide-Ranging Achievement Test–Revised (WRAT-R33). Reading achievement was assessed in Cohorts 1 and 3 at ages 11, 14, 17, and 20, and in Cohort 2 at age 20. Writing and math were assessed in Cohorts 1 and 3 at ages 14 and 20, and in Cohort 2 at age 20. Cognitive ability scores were also averaged across age (intelligence test-retest ICC range = .82–.90; achievement test-retest ICC range = .84–.88).
