Modified logit life table system: principles, empirical validation, and application

Despite its widespread use, the Coale–Demeny model life table system does not capture the extensive variation in age-specific mortality patterns observed in contemporary populations, particularly those of the countries of Eastern Europe and populations affected by HIV/AIDS. Although relational mortality models, such as the Brass logit system, can identify these variations, these models show systematic bias in their predictive ability as mortality levels depart from the standard. We propose a modification of the twoparameter Brass relational model. The modified model incorporates two additional age-specific correction factors (γx and θx) based on mortality levels among children and adults, relative to the standard. Tests of predictive validity show deviations in age-specific mortality rates predicted by the proposed system to be 30– 50 per cent lower than those predicted by the Coale–Demeny system and 15–40 per cent lower than those predicted using the original Brass system. The modified logit system is a two-parameter system, parameterized using values of l5 and l60.