The leading cause of death used to be infectious disease but has changed dramatically. Compression of morbidity people would remain healthy longer, until a few months before their maximum life span and would then die after a relatively short period of disability. Others have said that extension of morbidity people living longer with disabilities. Whether there is a maximum life span in humans has not been resolved. Half the world"s population of older adults live in developed countries and the other half in developing countries but this will change where by 2030, more than twice as many older people will be in developing countries. Demographic transition is used to describe the process by which a society or nation moves from one of high birthrate and high mortality to one of low birthrate and low mortality. Gender men and women used to have similar life expectancies largely due to infectious disease.