Phd in SCHOOL OF STATISTICAL SCIENCES

Thesis title: Understanding health dynamics among the oldest-old

In most developed countries, the proportion of oldest-old has increased during the last decades as a consequence of the decline in old-age mortality. An increasing number of oldest-old people will pose challenges for the health-care and economic systems of modern societies but it could be transformed into an opportunity from a social and economic perspective if those people succeed in aging healthily. Evaluating the health condition of the oldest-old is not straightforward as, especially for people in this stage of life, health requires to be analyzed by simultaneously considering multiple dimensions of health. For instance, health-care needs may be the result of a complex system of diseases, syndromes or other characteristics that is not satisfactorily described by a single aspect of health. Considering health holistically, by jointly analyzing several health measures, helps identifying health profiles that would allow to a better evaluation of the needs and a more efficient use of the resources. On the other hand, analyzing single objective health measures has the advantage of deepening the existing knowledge on the dynamic relationships between major health aspects, their deterioration and which factors are related to this process. The increasing presence of oldest-old people in modern societies implies a growing need of statistical information and indicators capable of monitoring the health conditions of those individuals. Over the last years researchers have tried to overcome the problem of scarce data availability on the health of the oldest-old by conducting specific surveys to reach those (not anymore) exceptionally old individuals to better understand the characteristics and dynamics of health among long-lived individuals. Self-rated health (SRH) is the most widely used indicator for assessing the general health status of a person: nowadays its related question is often included in general surveys and it has been harmonized to allow international comparisons. Understanding the mechanism that underlies the process of self-assessment of health is of great interest. It has been investigated both at the general population level and specifically on elderly individuals, however research on the oldest-old is still lacking. No matter which health dimension is analyzed, the socioeconomic status is always the first factor considered to explain health differences. Socioeconomic inequalities in health are well-known among the general population and the elderly. However, there is growing evidence that a socioeconomic gradient in mortality persists also at very old ages suggesting the need for further research to verify whether socioeconomic differences in health persist among the oldest-old. The aim of this PhD thesis is to contribute at partly filling the gaps in oldest-old research by investigating (a) the health conditions in which people reach very old ages especially if considering health holistically; (b) the dynamic relationship between two major health aspects such as physical ability and cognition, their deterioration and which factors are related to this process; (c) the mechanism underlying the self-assessment of health; and (d) whether socio-economic health inequalities persist among nonagenarians. Each of the first three research questions (a, b and c) corresponds to a chapter of the thesis while the forth one (d) is investigated across all of them. Different data sources were used in the PhD thesis. Data from the Mugello Study were used to answer research questions (a), (c) and (d) and data from the 1905 Danish Cohort Study were used to answer research questions (b) and (d). Each of the research questions were addressed by performing the most appropriate methods to address specific issues. Considering health holistically, by analyzing several health dimensions, allowed us to identify heath profiles that are expected to have different health-care needs. Moreover, individuals with certain demographic and socioeconomic characteristics were more likely to be characterized by one or another health profile. Analyzing the deterioration of specific dimensions of health, as physical ability and cognition, resulted in finding a dynamic relationship between two important aspects of health. Their deterioration process does not follow the same path, even though the socioeconomic and lifestyle factors related to both measures are similar. Self-rated health among the oldest-old seems to have a similar hidden structure compared to the one of elderly people. Functional and emotional health play an important role, while socioeconomic characteristics only affect the process of self-assessment of health indirectly via the functional component. Overall, socioeconomic inequalities in health persist among the oldest-old independently on the way health is measured. More studies on the health conditions of oldest-old people, a growing segment of the population in developed country, are necessary to shed lights on many important aspects of health and the health-related factors. In a context of resources that are becoming scarcer and scarcer, this could help policy makers to drive their interventions to the most stringent issues and face them on time to adopt better strategies to cope with the challenges posed by the greater presence of oldest-old in the societies.