Incidence of dementia in a representative British sample

In a four-year follow-up study of 1042 elderly people (aged 65 years or older), randomly sampled from the community, levels of dementia were assessed using a two-phase case-finding procedure (screening followed by clinical interview) among survivors. Clinical information on those not reinterviewed was provided by death certificates, hospital case notes, or postal questionnaires. The weighted four-year cumulative incidence of dementia was 3.7% (95% confidence intervals: 2.4%-5.0%), with age-specific rates of 0.9%, 2.8%, 5.2%, 9.0%, and 8.7% for the age groups 65-69, 70-74, 75-79, 80-84, and 85-89 years respectively. While consistent with data from other British regions, it remains likely that these rates underestimate true incidence.