The epidemiology of dementia: GMS-AGECAT studies of prevalence and incidence, including studies in progress.

The paper reviews the main studies using the AGECAT computerised diagnostic system for the diagnosis of dementia in community studies of prevalence and incidence. It is suggested that variations in reported rates may be due to the use of unstandardised methods, and the paper reviews the oldest established standardised interview: the Geriatric Mental State. The AGECAT system is outlined, and the studies of its diagnostic validity indicated. Arguments are presented against the inclusion of cognitive tests in such instruments, and for the critical evaluation of the concepts of mild dementia. The use of AGECAT in the US/UK Diagnostic Project, and in the Liverpool study of Continuing Health in the Community is described. In addition, preliminary information is given on the Liverpool ALPHA study, the MRC UK multi-centre study, studies organised by the Pan American Health Organisation (Argentina, Chile, Cuba), the Eurodem concerted action (based in Rotterdam) and the WHO multi-site studies. Individual studies in Spain and Portugal are also discussed.