Biomedical and social determinants of cognitive impairment in the elderly.

Studies in age-related cognitive changes do not necessarily take into account the clinical and social phenomena associated with age that may have more effect on cognition than does psychologic senescence. Clinically inapparent biologic deterioration, drugs, mild dementia, and atypically presenting depression may influence cognition. Selection bias may skew the results of studies on the elderly when control groups are made up of undergraduates or of "normal" elderly whose normality is taken for granted rather than verified. The epiphenomena of aging, such as retirement, social isolation, and bereavement, which are not inherent in the aging process, influence cognition, as do labeling and learned helplessness. Laboratory-based tests of cognition may not sufficiently resemble real-life conditions to have validity. Future research will be shaped by how we conceptualize the relation between aging and intellectual function.