The Canadian Study of Health and Aging is a multicenter, population-based cohort study of dementia with a sample of 10,263 participants aged 65 or over. Field work began in 1991, and a follow-up study was undertaken in 1996-97. The present article describes the origins and objectives of the study, provides an overview of its design, organization, and data collection methods, and offers a brief summary of the main results.
The Canadian Study of Health and Aging was a large, multidisciplinary, national core study--with a number of "add-on" investigations--of the epidemiology of dementia and the health of older people. This structure was a fiscally prudent way to balance between mandated and investigator-initiated inquiry. In hindsight, several important features of the study would be repeated. Future studies might profitably consider a longer funding period for analysis, and a more strategic approach to in-depth, supplementary studies.
Correlates of nonparticipation in the community interview component of the Canadian Study of Health and Aging and their impact on bias in the results were analyzed. Characteristics of study subjects, their habitats, and encouragement techniques were analyzed to identify correlates of variation in response rates across the 18 study centers. Refusal rates from 14% to 41% varied by age, gender, city size, number of subjects and length of time for enrollment, and method of approach. Cognitively impaired subjects had higher refusal rates which affected prevalence estimates. At one study site, efforts to "convert" subjects who initially refused to participate in the survey were successful with 26% of those who were recontacted.
The Canadian Study of Health and Aging collected data focusing on the epidemiology of dementia, using interviews and questionnaires, clinical and neuropsychological examinations, physical measurements and blood collection, and access to public records such as death certificates, from people 65 and over in community (N = 9,008) institutional settings (N = 1,255). The study produced 12 data sets, including community health interviews, clinical and neuropsychological assessments, risk factor questionnaires, and caregiver interviews. This report describes the data collection and processing procedures, summarizes the content of each data set, and outlines the information collected in sufficient detail to permit its suitability for secondary analyses to be scrutinized.
The Canadian Study of Health and Aging produced an estimate of the incidence of dementia among elderly Canadians by following up, after 5 years, the undemented found in an initial prevalence survey. Initial and follow-up estimates could be biased by false-negative error in the screening tool used for subjects living in the community, and by erroneous classification of subjects who died in the interim. Here, we use a deterministic model to quantify those possible biases. We conclude that, using the estimates of the errors from control samples, the incidence among community subjects would be overestimated by 15%, and the incidence among the institutional subjects would be underestimated by 37%. The overall incidence would be underestimated by 14%. Most of the bias can be attributed to inaccuracies in the classification of deaths.
There was a five-year delay between the two waves of the Canadian Study of Health and Aging during which 2,982 participants died. Their cognitive status before death should be taken into account in estimating the incidence of dementia in the cohort. Information concerning antemortem cognitive status was available from death certificates and from an interview with a close relative of the decedent at the CSHA-2 follow-up. The interview included a direct question on whether the person had been diagnosed with dementia and questions covering cognitive signs and symptoms from which we formed an algorithm to predict probability of dementia. These sources of information were validated using a small sample of study participants who died within five months of undergoing the CSHA clinical examination. Sensitivity of the death certificate and the question regarding diagnosis of dementia was low (33% and 44%), although their specificity was very high. Accordingly, we combined these with the predictive algorithm to form an overall estimate of the probability of antemortem dementia. This raised the sensitivity to 82% (specificity 93%).
The Canadian Study of Health and Aging was a complex undertaking that faced management challenges not encountered by smaller-scale projects. The study followed 10,263 elderly people in 18 study centers spanning six time zones; it was administered in two languages, and over 70 investigators were involved. The data collected from each participant were not fixed, but varied according to the results of earlier testing. The data could include a screening interview, a self-completed risk factor questionnaire, an interview with a relative, a clinical examination, neuropsychological testing, blood samples, and neuroimaging. This report describes the approach taken to organize the study, to track participants, and to monitor adherence to the study protocol. It also describes the human organizational aspects, including systems for staff training, for communicating among study centers, and for coordinating the publication of results. The discussion proposes some guiding principles for administering multicenter studies.
The Canadian Study of Health and Aging drew representative samples of people aged 65 or over from the community and institutions across Canada. The sample was designed to provide regional and national prevalence estimates for dementia by age and sex. Thirty-six sampling areas were used in a stratified cluster design with optimal allocation; sampling weights were developed to provide population estimates. The sample included 9,008 people aged 65 or over from the community, and 1,255 from institutions. This report describes the sampling procedures, the methods used to recruit people to the study and participation rates, the characteristics of the resulting sample, and the way in which sample weights should be used.