Statistical Demography


Joint Models for Investigating Fertility and Mortality Rates

Jutta Gampe, Marie Böhnstedt, Ralf Schaible

Detailed description:

Fertility and mortality are interdependent processes. Dependence may be in the direction of increased mortality due to the costs of reproduction, or it may be in the opposite direction due to individual capacities that allow for high levels of reproduction to go along with lower mortality. Understanding these mechanisms is essential in biodemography.

When the patterns of age-specific fertility and mortality for some species are unknown and need to be estimated, this interdependence between the processes also introduces some extra complications in the statistical approach: the terminal event (death) is not independent of the recurrent event process (reproduction); conversely, fertility constitutes an internal time-varying covariate process for survival. So-called joint models (i.e., for the recurrent event process and the survival process) are required to produce unbiased estimates of age-specific fertility rates and death rates. Such models also allow us to assess the dependence between the two processes.

This project develops estimation strategies for joint models for data derived from experiments in the Institute’s Laboratory of Evolutionary Biodemography, in which reproductive outcomes are recorded as individual interval-counts of produced offspring. The studies are characterized by modest sample sizes, and have to incorporate the effect of different treatments (for example, feeding regimes) that influence both processes in the model.

Research keywords: Statistics and Mathematics; Biodemography