Estimates of the prevalence rate of dementia in those aged over 65 and living in the community vary widely, from 0.5% to 6.3% for mild dementia, and from 1% to 7.4% for moderate or severe dementia. These figures have usually been obtained by screening and refer to non-specific dementia syndromes. Few studies have gone further to provide a detailed diagnostic breakdown on this cross-sectional detail, or followed patients up to obtain longditudinal data. Those that have provided further information have not provided full diagnostic profiles of unselected samples, leading to the likelihood of bias in the results.