The sex differential in mortality: a historical comparison of the adult-age pattern of the ratio and the difference

The ratio (RMR) is the standard measure of sex differentials in mortality. It is commonly known that the RMR was historically small and increased throughout the 20th century. However, numerical properties might account for the trend in the RMR rather than sex differences in risk factors. In this study we examine the age pattern of the absolute difference in male to female mortality rates (DMR) as an alternative measure in a historical context and compare it to the RMR pattern. Whereas the RMR is close to one at every age in the 19th and early 20th century and increases until the present day, the adult age pattern of the DMR is relatively stable throughout the last 150 years. We also found that the DMR is approximately exponentially increasing from age 40 to 90, implying a universal biological force behind sex differentials in mortality. However, interactions between biology, behavior and environment are complicated and have to be considered when interpreting these findings. Moreover, between ages 15 and 40 the DMR declined in the second half of the 20th century, whereas the RMR increased. Hence, the trend in the latter measure is likely to be an artifact of very different mortality regimes between populations. Therefore, we argue that it is necessary to consider both measures when conducting comparative analyses and to be careful in interpreting their time, cross-cultural and age trends, since they can lead to different conclusion about sex specific underlying risk factors.