Provocative international disparities reported in the prevalence rates of dementia and depression require further investigation. This is the first psychiatric study, to the best of our knowledge, about the prevalence of DSM-III-R dementing and depressive disorders and their relationships in a representative, stratified community sample of the elderly in both a Spanishspeaking country and southern Europe.
A two-stage screening was completed in 1080 elderly. Sampling with replacement was done, and the cumulative response rate was 88%. In phase 1, lay interviewers administered the Spanish versions of the Mini-Mental State examination and the Geriatric Mental State Schedule—Automated Geriatric Examination for Computer Assisted Taxonomy package. In phase 2, research psychiatrists administered the same instruments and the History and Aetiology Schedule to all the probable cases and a similar number of randomly selected, probably normal subjects.
An estimated 5.5% of the elderly were considered to have a dementing disorder, the most prevalent types being primary degenerative dementia, Alzheimer's type (4.3%), and multi-infarct dementia (0.6%). Depressive disorders were found in 4.8% of the elderly. Psychiatric morbidity, specifically depression, was associated with lower educational levels. "Case levels" of depression were documented in 25.4% of the demented cases and case levels of "organic" disturbance were seen in 18.2% of cases of major depression.
Among the elderly, the prevalence of Alzheimer's disease and multi-infarct dementia, as opposed to depression, increases steeply with age. The overlap found between dementia and depression may have nosological implications. There could be an effect of lower education levels on psychiatric morbidity, particularly on depression.