Population Heterogeneity, Late-Life Mortality Deceleration,

Mortality Levelling-off, Mortality Plateaus

Here are some key references to pioneer scientific publications, which first introduced the idea of population heterogeneity (gamma-distributed individual risk) to explain a logistic function for mortality rate, late-life mortality deceleration, mortality levelling-off, and mortality plateaus:

This logistic model with gamma distributed individual risk and late-life mortality deceleration became widely known to biologists and demographers in 1971, when Dr. Beard published a detailed review of his studies in the book "Biological Aspects of Demography":

The heterogeneity mortality model with gamma distributed individual risk (producing logistic function for mortality rate) was developed by famous British statistician and actuary Robert Eric Beard in 1959.   Dr. Beard also became famous for his book "Risk Theory", which had three editions:

Beard, Robert Eric (1911—1983)