Diagnoses of dementia and depression: a latent trait analysis of their performance

Four diagnostic systems for dementia and depression are compared on a community sample of 274 subjects. They are: DSM-III, Gurland's system, AGECAT and a clinician's ratings. These are compared, not in the usual terms of prevalence rates and cross-tabulations of diagnostic categories, but by examining the performance of each system in terms of hypothetical, continuously distributed traits underlying the symptoms of dementia and depression, as in the latent trait model described by Duncan-Jones et al. (1986). Each diagnosis is characterized by the level of severity (threshold) at which it operates, and its accuracy. Evidence is given to support a dimensional view of dementia.