Nouveaux regards sur la longévité : analyse de l'âge modal au décès et de la dispersion des durées de vie selon les principales causes de décès au Canada (1974-2011)

The mortality decline among the elderly witnessed in most developed countries since the mid-twentieth century has brought upon important changes in the age distribution of deaths, as mirrored by its gradual shift to older ages and its concentration into a progressively shorter age interval. These transformations are the result of underlying changes in the mortality profile by age and cause of death, a subject which has received very limited attention in the current literature. The main objective of this thesis is to examine changes underwent in the age-at-death distribution in low-mortality countries, particularly in Canada, along a cause-of-death dimension. The second objective is to conduct a Canada-U.S. comparative analysis to determine whether Canadian trends in M and SD(M+) are country-specific or if a similar pattern is observed in other low mortality countries, more particularly in the U.S.  These evolutionary changes are monitored through the lens of new mortality indicators, the modal age at death, M, and the standard deviation beyond the mode, SD(M+). Their estimation relies on the use of the P-spline nonparametric smoothing approach that we specifically adapted to the context of cause-of-death analysis. The results, presented in three scientific papers, are obtained using data from the Canadian Vital Statistics Death Database of Statistics Canada, the National Vital Statistics System of the  National Center for Health Statistics, and the Human Mortality Database. We focus on six leading causes of death in Canada and the U.S., that is heart diseases, cerebrovascular diseases, colorectal cancer, lung cancer, prostate cancer (males), and breast cancer (females).  Findings from the first paper reveal a steady upward trend in M values for all leading causes of death since the mid-1970s in Canada. Moreover, the increase in cause-specific modal age estimates occurred at a strikingly similar pace for most causes, except for heart diseases (males) and breast cancer (females). However, the various causes studied differ greatly in terms of levels. In general, the following ranking (from lowest to highest modal age values) is observed: lung cancer, colorectal cancer, heart diseases, and cerebrovascular diseases. For males, prostate cancer ranked in between the two sub-categories of cardiovascular diseases until the end of the 1990s and in between colorectal cancer and heart diseases after that. For females, estimates for lung and colorectal cancer bound those for breast cancer. The main results from the second paper suggest a decline in old-age lifespan variation for leading causes of death among Canadian males and females, as reflected by downward trends in cause-specific SD(M+) values over the period 1974-2011. However, the five leading causes of death differ greatly in terms of variability at older ages. Since the early 1990s, the two main sub-categories of cardiovascular diseases exhibited lower variability in ages at death compared to the four types of cancers studied, except for prostate cancer. Indeed, throughout the study period, the level of SD(M+) for this type of cancer was similar to that observed for cerebrovascular diseases. Notable differences in variability of ages at death have also been observed among the four types of malignant neoplasms selected. For both sexes, deaths attributable to lung cancer spread over a wider age interval than those for colorectal cancer, whose dispersion of deaths is higher than prostate cancer (males) and lower than breast cancer (females). The Canada-U.S. comparative analysis, presented in the third paper, revealed small differences between Canada and the U.S. in M and SD(M+) trajectories by leading causes of death. Indeed, in the U.S. as in Canada, modal age at death values for each leading cause increased throughout the 1974-2011 period while variability of deaths occurring at ages above the mode decreased. Moreover, the various causes studied ranked similarly in the two countries based on their respective M and SD(M+) values. This analysis also showed negligible age-specific mortality differentials between the two North American countries' elderly for most causes studied, except for lung cancer (males) and breast cancer (females). These differences are explained in part by health-related behaviors - since lung cancer and, to some extent, breast cancer too are behavior-driven diseases - as well as socioeconomic differences in access to health care. Trends in cause-specific M and SD(M+) values suggest that the old-age compression of mortality regime is at work since the mid-1970s for each leading cause of death among Canadian males and females. Moreover, it appears that women have recently entered the era of the shifting mortality regime. The analysis for the U.S. over the same period shows comparable outcomes therefore indicating that this situation is not specific to the Canadian context.

Keyphrases: Cancers, Canada, Longevity, Modal age at death, Old-age mortality compression, Variability in ages at death, Causes of death, Cancers, Cardiovascular diseases, P-spline smoothing, Canada, U.S.