Effects of screening errors and differential mortality on the estimation of the incidence of dementia in the Canadian Study of Health and Aging.

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.

Study sampling in the Canadian Study of Health and Aging.

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.

Correlates of nonparticipation in the Canadian Study of Health and Aging.

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.

Estimating antemortem cognitive status of deceased subjects in a longitudinal study of dementia.

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%).

Demodex folliculorum and Demodex brevis in cutaneous biopsies.

The hair follicle mites Demodex folliculorum and Demodex brevis are ubiquitous obligatory ectoparasites of man. We studied these mites in a consecutive series of skin biopsies submitted to a dermatopathology laboratory; 10% of all biopsies and 12% of all follicles contained demodectic mites. The prevalence of both species increased with age, but D. brevis had a lower prevalence. The face was most heavily infested by both species, but D. brevis had a wider distribution on the body. Males were more heavily infested than females with both species, the difference being strongest for D. brevis. Other ecologic characteristics noted include the type of follicles infested, follicular dilation, perifollicular inflammation, and the presence of a dense homogeneous eosinophilic material surrounding the mites. These data confirm ecologic and epidemiologic differences between the two species and emphasize that they should be distinguished in future studies of the roles these mites may play in a variety of disease states.