The incidence of dementia in Canada. The Canadian Study of Health and Aging Working Group.

OBJECTIVE: To estimate the incidence of dementia, including AD, among Canadians aged 65 and over. METHODS: A 5-year cohort study of 10,263 seniors was undertaken, including community and institutional samples. The baseline study in 1991 identified 1,132 prevalent cases of dementia through screening and clinical examination. The remaining 9,131 cases formed the incidence study sample and were rescreened and selectively reexamined in 1996. Incident cases were diagnosed using established criteria. Incidence was estimated based on the 1991 population, and included data on those who died between the first and second phases of the study. RESULTS: Of the nondemented cohort who remained alive in 1996, 5,432 people in the community (88.3%) and 210 (91.3%) in the institutional sample participated in the incidence study. Nine hundred sixty incident cases were identified; the overall age-standardized incidence rates were 21.8 (women) and 19.1 (men) per 1,000 nondemented persons per year. This translates into 60,150 new cases of dementia per year in Canada. The logarithm of the rates rises linearly with age, but suggests a slight slowing of growth in incidence in the oldest age groups. CONCLUSIONS: Our incidence estimates lie toward the upper end of the range of incidence estimates found in other studies. Nonetheless, we calculate that several factors may have biased our estimates downward, suggesting that the incidence of dementia may be higher than many studies have reported.