Human longevity has always been a central focus of demographic research. It reflects the intensity, age pattern, and causes of mortality throughout the life cycle, from infant mortality to old-age mortality and everything in between. The objective of this research project is to develop and apply new mathematical tools for the sensitivity analysis of longevity. Sensitivity analysis quantifies the effects of changes, and these new tools will enable researchers to quantify the effects of changes in mortality on various statistics measuring longevity. Those statistics include life expectancy, indices of variation in longevity, and the contributions of particular causes of death to those statistics.
Sensitivity analysis is important in the study of longevity because human mortality has changed dramatically over the last two centuries, due to unprecedented advances in medicine, public health, and technology. In addition to these temporal changes, at any one time, patterns of longevity also differ among regions, countries, and socio-economic groups. Together, these changes in longevity have important implications for society, determining, as they do, the age structure of populations and the needs for medical care and social services. The new analytical methods developed in this research will be widely useful in studies of changing longevity and its consequences.
Recent years have seen dramatic changes in longevity: across the world, people are living longer, and the distribution of ages at death has narrowed. These changes have great social, economic, cultural, and medical impacts, and the goal of this study was to provide a tool for one specific kind of analysis to help researchers understand them. That tool is called sensitivity analysis. When demographic data are analyzed, the results include values of parameters (such as the mortality rate at every age). Sensitivity analysis asks, and answers, the question of how changes in those parameters would affect the mean, and the variation of longevity. Given the recent dramatic changes in mortality and longevity, sensitivity analysis is a crucial component of demographic analysis. This project has produced results on three different aspects of sensitivity analysis. First, we produced sensitivity analysis for a number of measures of the variation in longevity among individuals, and applied this to data on current and historical populations. Second, we developed the theory necessary to extend sensitivity analysis to studies that investigate mortality by cause of death. With these results, we are now able to see how changes in mortality due to specific diseases will change patterns of longevity. Third, we developed a new approach to the sensitivity analysis of population projections (the models that governmental and international bodies use to predict future population size and composition). Our results will make it possible for demographers to explore the effects of changes much more deeply than ever before. The results have been presented at national and international conferences. Some have been published in scientific journals, and others are currently being prepared for publication.
