Leader: Elisabetta Barbi (Sapienza); Other collaborator(s):
Impressive progress has been achieved in reducing mortality, also at advanced ages, at least until the Covid-19 pandemic. As further progress is to be expected in the future especially at older ages, the number of long-lived individuals will continue to increase. To understand the mechanisms thanks to which these improvements are achieved, we aim to estimate the rate of senescent mortality by age (or “rate of ageing”). A recent theory suggests that the rate of aging may be the same for all human beings: progress in survival can be achieved by lowering the level of mortality (individual death rates) but not by slowing down the speed of the basic ageing process itself.
Brief description of the activities and of the intermediate results: Task 1 focused on modelling mortality trajectories at old and extreme ages. A preliminary formal analysis of the theoretical predictions of the Gamma-Gompertz model, a popular model for the analysis of mortality at old ages, showed that this model does not fully capture all the qualitative characteristic of the observations at the extreme ages. Thus, possible extensions of the Gamma-Gompertz model have been explored in order to fully capture the behaviour of the mortality trajectory at these ages. An analysis focusing on old age mortality of Italian cohorts born at the beginning of the XX century have been performed. Death rates for ages 60 to 105 have been obtained from the Human Mortality Database (HMD, www.mortality.org). Ages at death over 105 are taken from a specific survey for the collection and the validation of individuals aged 105 and over (ISTAT). Mortality trajectories have been modelled under the frailty model setting. The Gamma-Gompertz model has been extended to background mortality, that is the component of mortality which is unrelated to senescence, but it may still vary with age as well as over time. Furthermore, the Gompertz rate at which mortality increases with age has been decomposed into two components, the so-called rate of individual ageing and the rate of mortality progress. The enhanced frailty model seems to better capture the qualitative features of the mortality trajectories. Exploratory applications of the model to updated Italian mortality data show that the trajectory of mortality actually decelerates and reaches a plateau, as found in previous studies, but both the age at the deceleration and the age at the plateau move toward increasingly advanced ages as mortality at earlier ages decreases.
Main policy, industrial and scientific implications: Information on the behavior of the force of mortality at extremes is essential to shed light on human ageing and longevity, and the mechanisms of mortality improvements. An important implication of the plateau is that individuals who survive to advanced old age would do so because they reach older ages in better health and not because they age more slowly. This is because the levelling off of mortality rates is mathematically plausible if individuals differ in their level of deterioration but not in their rate of deterioration. Moreover, a mortality trajectory such as that estimated from Italian data, and its dynamics over time, contrasts the idea of an foreseeable limit to human lifespan and supports instead the possibility of further continuous improvements in survival at older ages. This has important consequences in the society, economics, and policy.
In the period July-September 2024, the members of Task 1.1 devoted most of their efforts to dissemination activities. We cooperated in the preparation of the WP1 Policy Brief, and we prepared a manuscript aimed at promoting a positive approach to demographic change in Italy (ageing) that will be published in number 4/2024 of “Il Mulino” (Journal), presumably by the end of the year. We were also deeply involved in the organization of the Spoke 1 Conference that was held in Rome on 3-4 October 2024 (first day in Sapienza University, at the Department of Statistical Sciences and second day at Istat).
In the last trimester of 2024, members of Task 1.1 participated in the "StaticAll - Festival della Statistica e della Demografia" that was held in Treviso on 17-20 October 2024. Their main activities were: 1) oral presentation and ensuing debate on the theme: “Think Demography, Think Positive! Una lettura positiva dell'invecchiamento della popolazione”, and 2) a series of laboratory initiatives targeted to students, to make them aware of the issues related to longer survival and population ageing.
In November, Task 1.1 started a collaboration with colleagues from Odense University to perform statistical analyses on semi-supercentenarians (105-109 years) at aggregate and individual level. To this end, several meetings were held both online and in person at the Department of Statistical Sciences of Sapienza University.
Coming soon