Prevalence of senile dementia in Okinawa, Japan. COSEPO Group. Study Group of Epidemiology for Psychiatry in Okinawa.

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.