MODELING AGE-SPECIFIC RISK - APPLICATION TO DEMENTIA

We give up-to-date methods for estimating the age-specific incidence o f a disease and for estimating the effect of risk factors. We recommen d taking age as the basic time scale of the analysis; then, the hazard function can be interpreted as the age-specific incidence of the dise ase. This choice raises a delayed entry problem. We present three meth ods: the person-years method; the smoothed Nelson-Aalen estimator, and the penalized likelihood approach. When explanatory variables are ava ilable, the Poisson model and the Cox model with delayed entry may be used for estimating relative risks; the penalized likelihood approach can also be used. We apply these methods to estimate the age-specific incidence of dementia using data from a large cohort study, Paquid, Th is 5-year study followed a random initial sample of 3675 subjects with 190 incident cases of dementia. We compare the estimates based on the three possible methods. The estimated incidences computed separately for men and women cross and it is verified that a non-proportional haz ards model for gender holds; women below 75 have a lower risk than men while women above 75 have a higher risk. (C) 1998 John Wiley & Sons, Ltd.