Mortality-rate crossovers and maximum lifespan in advantaged and disadvantaged populations: accelerated-mortality and sudden-death models.
One population is advantaged relative to another by our definition if its survival function is greater at all ages. A population has a lifespan maximum if there is an age at which its survival function becomes exactly zero. Earlier work concerned conditions under which the mortality-rate functions of advantaged and disadvantaged populations displaying lifespan maxima always crossed. Here two survival models of populations having lifespan maxima are presented in which mortality-rate crossings between advantaged and disadvantaged subpopulations may fail to appear. One, the accelerated-mortality model, has a continuous survival function; in the other, the sudden-death model, the survival function is discontinuous. Both differ from examples examined previously in that their mortality-rate functions become infinite at their lifespan maxima.
Hirsch
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Department of Physiology, University of Kentucky, Lexington, KY 40536-0298, USA.
Liu
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Witten
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D000818:Animals; D003645:Death, Sudden; D004777:Environment; D006801:Humans; D008136:Longevity; D015233:Models, Statistical; D013045:Species Specificity; D015996:Survival Rate