Twins: cognitive patterning and development as measured on the Wechsler preschool and primary scale of intelligence

Abstract

Cognitive patterning and development was appraised for 142 pairs of twins at 4, 5, and 6 years of age, based on their test scores on the WPPSI. Compared with singletons the twins showed an initial lag at age 4, with V-IQ more depressed than P-IQ, but by age 6 the deficit was fully recovered. MZ twins displayed high within pair correlations for V-IQ and P-IQ at age 4, and the correlations further increased by age 6 as the measures of IQ became stabilized. MZ twins also showed significant concordance for the patterning of subtest scores. DZ twins displayed moderate within pair correlations for IQ which declined somewhat over age, and which fell significantly below the MZ correlations. Measures of family socioeconomic status and parental education correlated 0.28-0.32 215=a with the twins' IQ at age 6. The results indicated that within broad range of home environments, the genotype exercised a profound influence on childhood mental development. It was coded not only for a general factor, as represented in Full Scale IQ, but also for the differential strength of the composite abilities which were separately measured on the Verbal and Performance Scales. In addition, the genotype was coded for the patterning of relative strengths and weaknesses as revealed on the individual subtests.