A community based study of the incidence of dementia in subjects aged 85 years and over.

The aim was to investigate the incidence rate of dementia for community residents aged 85 years and over. It was a two wave community study of 224 subjects (community residents including those residing in a nursing home) older than 85 years, restudied 4.1 years after a community prevalence study. A two stage method was used, comprising the mini mental state examination followed in a stratified sample by the geriatric mental state schedule (A3)/AGECAT. Incidence rates were based on person-years at risk. The overall incidence of dementia was 6.9 (95% confidence interval (95% CI) 4.8-9.1) per 100 person-years at risk. The incidence was significantly higher for women than for men; respectively 8.9 (95% CI 5.9-11.9) v 2.7 (95% CI 0.5-4.9) per 100 person-years at risk. In the fastest growing age group seven out of 100 persons develop dementia each year. Women, who constitute two thirds of the oldest old, seem to have a higher risk. Further research is needed into the risk factors for dementia in this age group.