New Estimates of Mortality Trajectories at Extreme Old Ages

A growing number of persons living beyond age 85 underscore the need for accurate measurement and modeling of mortality at advanced ages. This is also very important issue for making correct forecasts of population aging and related demands for medical services and social support. Earlier studies indicate that exponential growth of mortality with age (Gompertz law) is followed by a period of mortality deceleration with slower rate of growth. This study challenges earlier conclusions with new data and estimates. In this study we used U.S. cohort survival data for people born in the same calendar year. For this purpose we obtained data from the U.S. Social Security Administration Death Master File to estimate hazard rates for 15 single-year extinct birth cohorts born in 1881-1895. We found that mortality deceleration is far less pronounced when it is measured for shorter monthly age intervals rather than for traditional annual intervals. To find out why does it happen we have made a simulation study and found that traditional measures of hazard rate (like the Nelson-Aalen hazard rate estimate) underestimate mortality force at extreme old ages (underestimation bias) when death rates are exceptionally high. We also found that mortality deceleration is far less pronounced when datasets with higher data quality (age reporting) are analyzed.