Heterogeneous ability profiles may be a unique indicator of impending cognitive decline.

OBJECTIVE Prior research has found that within-person standard deviations across different neuropsychological domains are larger in various clinical groups than in healthy control groups, but little is known about the specificity of these measures to clinical conditions. METHOD Within-person standard deviations were computed across composite scores representing episodic memory, perceptual speed, inductive reasoning, and spatial visualization and compared in older adults differing in the amount of subsequent cognitive change, and as a function of age in a large sample of adults ranging from 18 to 89 years of age. RESULTS The standard deviations at an initial occasion were significantly greater in older adults who experienced the most negative longitudinal change, but relations of the standard deviations with age were only evident in adults under 65 years of age, and they were negative rather than positive. CONCLUSIONS These findings suggest that high values of within-person variability may have specificity in predicting late life cognitive decline.