Change in depressive symptoms in the Baltimore longitudinal study of aging.

Depressive symptoms have been represented in the research and clinical literature in terms of both an episodic phenomenon and as enduring individual differences. We investigated depressive symptoms longitudinally in a sample of older adults. Participants were 737 individuals (M(Age) = 73 years initially, 39% women) in the Baltimore Longitudinal Study of Aging who provided biennial Center for Epidemiological Studies-Depression data on up to five occasions over an 8-year period. We found both trait and state-residual variability, with symptoms increasing longitudinally on all subscales and accounting for an approximately 1-point increase per decade. Trait-like variability accounted for at least two thirds of the reliable variance. Interindividual differences were consistent over time, but occasion-specific variability diminished across occasions.