The contribution of general intelligence to cognitive performance across the lifespan: A differentiation analysis of the wechsler tests.

Human cognitive abilities exhibit positive interrelationships that can be represented by a latent general intelligence factor (g). Differentiation hypotheses propose that there are systematic interindividual differences in the strength of g, specifically along the dimensions of ability level (ability differentiation) and age (age differentiation). Despite the potential implications for cognitive theory and assessment, the available evidence on the matter is inconclusive. We present comprehensive analyses of differentiation effects across the lifespan, drawing on the meta-analytic integration of nonlinear factor analyses with German standardization samples (N = 4,129) of the most widely used intelligence tests worldwide (i.e., the Wechsler tests). Results support ability differentiation at all ages, with particularly large effect sizes in young adults, and suggest a complex pattern of age differentiation and dedifferentiation across the lifespan. These findings challenge the uniformity of g, highlighting the need to account for differentiation effects in cognitive theories and assessment. (PsycInfo Database Record (c) 2025 APA, all rights reserved).