life expectancy at age has been increasing steadily since the s by about one year per decade accordingly life expectancy at birth for women is almost always higher than for men central to this transformation has been the epidemiological transition from predominantly infectious causes of death to a predominance of deaths due to chronic and degenerative diseases the epidemiological transition also entailed a shift in the age pattern of mortality from one in which childhood diseases and deaths were common to a situation where disease and mortality are highly concentrated at older ages