METHODS:

The prevalence of dementia was investigated in Okinawa Prefecture, Japan. In all, 3524 subjects, > or = 65 years old, were sampled randomly (urban and rural populations 61.1% and 38.9% respectively). Phase 1 of the survey was carried out by specially trained students of the Faculty of Medicine who used the Mini-Mental State (MMS) scale (interview rate: 94.3%) to screen 522 (15.8%) of the 3312 subjects for the phase 2 survey. Phase 2, conducted by psychiatrists using the Diagnostic and Statistical Manual of Mental Disorders (DSM-III-R) criteria, detected 172 cases of dementia.

RESULTS:

The estimated prevalence of dementia was 6.7%. For women, the rate increased sharply in the 90-99 year old group, and was 41.4%; for men in the 90-99 year old group prevalence was 21.2%. The ratio of Alzheimer-type dementia to multi-infarct dementia was 1.5:1 (men 1.2:1, women 1.7:1). The breakdown of the severity of dementia in the total cases was: mild 16.9%, moderate 30.8%, and severe 52.3%. The number of severe cases increased with age.