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• Demographers also study life expectancy, the estimated average lifetime of people born in a specific
year. Life expectancy can vary depending on:
1) Nation -- In 1998, the life expectancy at birth for a person born in the U.S. was 76.1 years, compared
to 80 years in Japan and less than 50 years in the African nations of Burundi, Chad, Rwanda, and
2) Sex -- Females born in the United States in 2000 have a life expectancy of about 80 years, whereas
men born in that year have a life expectancy of about 73 years.
3) Race -- African American men, for example, have a life expectancy at birth of about 65 years,
compared to 74 years for white males.
• Migration refers to the movement of people from one geographic area to another
• Migration can be voluntary (usually due to economic “push” and “pull” factors) or involuntary (forced
migration due to war or other social conflict)
• Immigration involves the movement into a geographic area, frequently to take up residency;
emigration refers to the movement of people out of a geographic area
• Today, about 900,000 people enter the U.S. each year
• More than 23 million people live outside their countries of origin
• Population Composition refers to the biological and social characteristics of a population, including
such attributes as age, sex, race, marital status, education, occupation, income, and size of household.
• The sex ratio is the number of males compared to the number of females
• In the United States, there are approximately 96 males to 100 females, due to women’s high life
• In India, there are approximately 107 males for every 100 females because women are more likely to
abort female fetuses and parents may provide less care for female children