Life expectancy is the number of years an individual can expect to live if conditions remain constant. Age at death varies tremendously from country to country and from group to group within a country.

In most countries, life expectancy increased dramatically during the 1900s due, in part, to fewer deaths among children and pregnant women. Public health measures such as access to clean water, sanitation, and vaccinations for children were largely responsible for improvements in health. Human immunodeficiency virus and acquired immune deficiency syndrome (HIV/AIDS), however, is decreasing life expectancy in some countries.

Females live longer at every stage of life and in almost every country. While the average global life expectancy is 68 years, it is about 70 years for women and 65 for men. Life ...