Aging and variability in performance

In this study we discussed conceptual issues regarding the definition of variability and investigated age-related differences in variability of performance. The following types of variability were defined: (a) diversity of the group or between-participant variability, which indicates the spread of participants within each group; (b) dispersion or within-participant variability, which indicates the spread of each participant's score; and (c) consistency of performance within and across test sessions, which indicates the stability of performance over time. It was hypothesized that the performance of elderly participants would generally be more variable. To assess the impact of task factors upon age-related differences in variability, several tasks varying in their psychomotor and cognitive demands were employed. The tasks used were choice reaction time (RT), finger tapping, and time estimation. There were no age differences in overall performance except on the choice RT task. The results indicated that variability is not a unitary phenomenon and that an age-related increase in variability is not observed for all tasks. Age-related differences in variability were observed for tasks where there were no age-related differences in overall performance. Whether or not age-related increases in variability were observed depended upon how variability was measured and upon task characteristics. Increased cognitive and motoric demands were associated with age-related increases in variability.