Groups versus individuals as the comparison unit in cognitive aging research

Abstract

A database containing speed and memory data from 362 adults ranging from 20 to 79 years of age was analyzed (a) to determine the nature of the normative cross‐sectional age trends for each variable and (b) to estimate the sensitivity of within‐individual comparisons for detection of age differences. The cross‐sectional results revealed largely monotonic, linear declines for each variable, a trend evident in each quartile of the sample of individuals from each decade. Because the consistency of scores from the same individual within the same measurement occasion was rather low, it was inferred that it may prove very difficult to detect the effects of aging within individual adults.