Biodemography of Mortality at Extreme Old Ages: A Study of Rodents and Humans

Natalia S. Gavrilova, University of Chicago
Leonid A. Gavrilov, University of Chicago

It is widely believed that the exponential growth of mortality with age (Gompertz law) is followed by a period of deceleration, with slower rates of mortality increase. This phenomenon was demonstrated for insects, worms and humans suggesting its general biological nature. In this study mortality deceleration was challenged by using large samples of survival records for laboratory mice and rats. The results on rodent data were supported by data on mortality of the U.S. birth cohorts demonstrating better fit by Gompertz model compared to Kannisto model. Simulations showed that some estimates of mortality as well as kernel smoothing of hazard rates may produce spurious mortality deceleration at extreme ages. This study suggests that mortality deceleration at advanced ages cannot be considered as a general biological phenomenon.