LONGITUDINAL AND CROSS-SECTIONAL TWIN DATA ON COGNITIVE-ABILITIES IN ADULTHOOD - THE SWEDISH ADOPTION TWIN STUDY OF AGING/

Cross-sequential methods of analysis. designed to separate age and coh ort effects, were applied to data from the Swedish Adoption/Twin Study of Aging. Thirteen cognitive variables were collected at 3 times of m easurement separated by 3-year intervals. Data were available from 85 individuals from monozygotic (MZ) pairs reared apart, 132 from MZ pair s reared together, 207 from dizygotic (DZ) pairs reared apart, and 178 from DZ pairs reared together (age range at first assessment: 41-84 y ears). Time x Cohort interactions were found for mean performance on 8 of the measures, revealing stable mean performance in the younger coh orts and longitudinal decreases in mean performance in the older cohor ts. Cohort and time effects for total variance were mixed; little evid ence was found for increases in variance with age. Age changes and coh ort differences in generic and environmental components of variance we re test-specific; several Cohort x Time interactions attained signific ance. Heritability of the general cognitive ability factor showed sign ificant longitudinal decreases over time in the older cohorts.