Patterns of intellectual development in later life.

Temporal changes in 16 measures of cognitive and intellectual functioning (11 Wechsler Adult Intelligence Scale subtests, 3 Wechsler Memory Test subscales, 2 measures of reaction time) were studied in the full data set from the First Duke Longitudinal Study of Aging. Patterns of change in these 16 measures were identified through a 'grade-of-membership' analysis -- a general model for identifying patterns in temporal variation that does not require parametric assumptions about the trajectory of change or assumptions about the homogeneity of the sampled population. The analyses showed that the temporal variation of the 16 measures could be described by five latent patterns that reflected the complex patterning of intellectual functioning in extreme late life. The relation of these five patterns of intellectual ability to age was examined, as were the relationships to measures of mental and physical health. These results underline the needs for comprehensive models of health and functioning in later life that describe changes in a multidimensional form.