In a heterogeneous cohort, the change with age in the force of mortality or some other kind of hazard or intensity of attrition depends on how the hazard changes with age for the individuals in the cohort and on how the composition of the cohort changes due to the loss of those most vulnerable...

At adult ages x, the force of mortality increases more or less exponentially with age, and the parameter associated with age, ?, can be used to gauge the rate of senescence (ageing) of a generation. The hypothesis has recently been advanced that the rate of senescence at the individual level may...