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Estimates of the prevalence rates for dementia vary significantly among countries. Such variation may be explained, at least in part, by methodologic differences in studies. The disparities in prevalence rates of dementia subtypes, particularly Alzheimer's disease and multi-infarct dementia, are especially apparent in studies conducted in Eastern and Western countries. In Japan and China, the prevalence of multi-infarct dementia exceeds that of Alzheimer's disease, whereas in the West, Alzheimer's disease predominates in the vast majority of studies. Clearly, cross-cultural studies of incidence using standard methods are needed to investigate whether a true difference in risk exists, and which risk factors differentially contribute to this variation. Migrant studies of genetically homogeneous populations offer a unique opportunity to answer these questions. This article explores the value of migrant studies, their application to etiologic questions of dementia and its subtypes, and recommendations concerning how to conduct such studies.

The Cognitive Abilities Screening Instrument (CASI) has a score range of 0 to 100 and provides quantitative assessment on attention, concentration, orientation, short-term memory, long-term memory, language abilities, visual construction, list-generating fluency, abstraction, and judgment. Scores of the Mini-Mental State Examination, the Modified Mini-Mental State Test, and the Hasegawa Dementia Screening Scale can also be estimated from subsets of the CASI items. Pilot testing conducted in Japan and in the United States has demonstrated its cross-cultural applicability and its usefulness in screening for dementia, in monitoring disease progression, and in providing profiles of cognitive impairment. Typical administration time is 15 to 20 minutes. Record form, manual, videotape of test administration, and quizzes to qualify potential users on the administration and scoring of the CASI are available upon request.