The diagnosis and grading of dementia in population surveys: measuring disability

Comparability in respect of severity of dementia and determination of the nature and degree of disabilities in daily living due to dementia are important in population-based surveys. In physical diseases impairment of a system or organ may be established independently of disability using the ICIDH framework but there are problems in measuring cognitive abilities apart from the characteristic behavioural limitations and aberrations that constitute the dementia syndrome. Both DSM-III-R and ICD-10 require as a criterion of dementia that social activities are interfered with, and the degree of dependency is the measure of severity. This suggests that assessment of disability should be the first objective, and the mental or physical causes uncovered next. A suitable informant may be the best judge of the nature of the disability. This procedure would show what services demented persons actually require, clarify the implications of dementia for estimates of active life-expectancy, and increase comparability between studies. Problems associated with this approach and the role of cognitive testing are briefly discussed.