Estimating the Lifetime Risk of Dementia in the Canadian Elderly Population Using Cross-Sectional Cohort Survival Data

Abstract

Dementia is one of the world’s major public health challenges. The lifetime risk of dementia is the proportion of individuals who ever develop dementia during their lifetime. Despite its importance to epidemiologists and policy-makers, this measure does not seem to have been estimated in the Canadian population. Data from a birth cohort study of dementia are not available. Instead, we must rely on data from the Canadian Study of Health and Aging, a large cross-sectional study of dementia with follow-up for survival. These data present challenges because they include substantial loss to follow-up and are not representatively drawn from the target population because of structural sampling biases. A first bias is imparted by the cross-sectional sampling scheme, while a second bias is a result of stratified sampling. Estimation of the lifetime risk and related quantities in the presence of these biases has not been previously addressed in the literature. We develop and study nonparametric estimators of the lifetime risk, the remaining lifetime risk, and cumulative risk at specific ages, accounting for these complexities. In particular, we reveal the fact that estimation of the lifetime risk is invariant to stratification by current age at sampling. We present simulation results validating our methodology, and provide novel facts about the epidemiology of dementia in Canada using data from the Canadian Study of Health and Aging. Supplementary materials for this article are available online.

KEY WORDS:

• Cross-sectional sampling
• Invariance
• Left truncation
• Loss to follow-up
• Point processes
• Stratified sampling

SUPPLEMENTARY MATERIALS

• Part A: Evaluating the behavior of the remaining lifetime risk estimator

• Part B: Investigating departures from (A3)

Additional information

Funding

The authors thank an Associate Editor, two referees, Mei-Cheng Wang and Micha Mandel for their insightful and constructive comments, Christina Wolfson for sharing her insight about the study design, and Bin Zhu for help in obtaining the data. MC was funded by NSERC, FQRNT, NIAID, and the Hopkins Sommer Scholars Program. MA was funded in part by NSERC, FQRNT, and the VA Health Services R&D Service. NPJ was funded in part by NIAID. The data reported in this article were collected as part of the Canadian Study of Health and Aging. The core study was funded by the Senior’s Independence Research Program through the National Health Research and Development Program (NHRDP) of Health Canada. Additional funding was provided by Pfizer Canada Incorporated through the Medical Research Council/Pharmaceutical Manufacturers Association of Canada Health Activity Program, NHRDP, Bayer Incorporated, and the British Columbia Health Research Foundation. The study was coordinated through the University of Ottawa and the Division of Aging and Seniors, Health Canada.