The prevalence of dementia in a total population: a comparison of two screening instruments.

Two short screening tests for dementia, the Information/Orientation (IO) sub-test of the Clifton Assessment Scale (CAPE) and the Mini-Mental State Examination (MMSE) were included in a survey of 1579 elderly people of a large general practice. All those scoring 21 and under on the MMSE, a one in two sample of those scoring 22, 23 and a one in ten sample of the remainder were investigated further using the Cambridge Examination for Mental Disorders of the elderly (CAMDEX). The prevalences of moderate to severe dementia and mild to severe dementia determined from the CAMDEX interview were 4.8% and 14.2%, respectively. For detection of moderate to severe dementia, a cut-point of 21/22 on the MMSE gave a sensitivity of 100%, specificity of 85% and an overall prevalence of 19.7%; mild to severe dementia was best detected by a cut-point of 23/24 giving a sensitivity of 89%, specificity of 81% and prevalence of 28.5%. A cut-point of 7/8 on the IO sub-test gave a sensitivity and specificity for detecting moderate to severe dementia of 87% and 97%, respectively, with a prevalence of 7.3%; for mild to severe dementia a cut-point of 10/11 gave a sensitivity of 67%, specificity of 94% and prevalence of 14.7%.