An uncertainty principle in demography and the unisex issue

"The purpose of this article is to show that if many characteristics affect the mortality of individuals, there are intrinsic limits to the ability of demographers to answer two elementary questions:" whether the force of mortality in the last year was more or less severe in one country relative to that in a second, and whether an individual's chance of survival would have been greater in one or the other of the two countries. The author notes that the conclusions are applicable to all demographic crude rates. "The possibility of encountering Simpson's paradox suggests that since sex is only one of many possible stratifying variables that appear to affect mortality, the use of mortality tables distinguished by sex and by no other variables is, in the absence of information about the importance of other variables, demographically arbitrary."