Do experienced diagnosticians agree about the diagnosis of dementia from survey data? The effects of informants' reports and interviewers' vignettes

Dementia in community settings is often diagnosed by computerized algorithm s. This study examines the extent to which independent diagnosticians agree d among themselves in diagnosing dementia, severity and type wizen presente d with data obtained during a population-based incidence study of cognitive decline and dementia, Secondly, it examines how judgements, based initiall y on respondents' self-reports and cognitive performance, were affected fir st by informants' reports and then by short case-vignettes written by train ed lay interviewers. Thirdly, it compares diagnosticians' diagnosis of deme ntia with the algorithmic diagnosis (AGECAT). The items presented were sele cted from two screening interviews at wave 1 and wave 2 separated by an int erval of 2 years and from wave 2 assessment and informant interviews, and i ncluded medical, psychiatric and ADL items and interviewers' own observatio ns. The sample (N = 42) was derived from the first year of the wave 2 asses sments, potential dementia cases entering consecutively while presumed norm als were selected randomly. Informants were available in 30. Agreement on d iagnosis and type of dementia improved with increasing information, particu larly from informants, but remained poor regarding severity. The number of cases of dementia, defined operationally, increased from 10 to 12 and uncer tain cases fell from eight to six, but no respondent initially diagnosed as a dementia case was rediagnosed as a non-case. or vice versa. Dementia typ e changed from agreement about Alzheimer's disease to agreement about vascu lar dementia in one case. Operational and algorithmic diagnoses showed good agreement. Causes of disagreement, the role of vignettes and the relevance of the results for population surveys are discussed. (C) 1998 John Wiley & Sons, Ltd.