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of variation in population change may lie in the volume and characteristics of immigration.
Population change inevitably has broad social and economic implications. Changes in the age composition of the population affect school enrollments and policies. The number and educational levels of the population in the early and middle adult years are critical for the future labor force and its productivity. And the numbers of elderly and how healthy they are become major determinants of pension needs and the health care system. Population change may also produce ripples across many other critical aspects of American life, in the needs for housing, the crime rate, savings, and voting.
Immigration has consequences for all these aspects of population change. In its relatively large flows and wide variety, immigration as the United States experiences it adds both to the numbers of people in the nation and to their diversity. Immigration works its longer-term effects through other dimensions as well.
First, not every group of immigrants into the United States bears children at the same rate. Immigrant groups with persistently high fertility rates will grow over time, absolutely and in relation to other immigrant groups. Second, not every group of immigrants has the same life span—that is, their mortality rates differ; these, too, may change over time and thus shift in their relation to one another.
If immigrants have a higher fertility rate than does the resident population, the nation will grow younger on average. And if immigrants have a higher mortality rate—that is, if they die at an earlier age—that trend will be reinforced. Again, the differences among groups of immigrants also matter, and so do the shifts within-groups and between groups as the generations unfold.1
Previewing the U.S. population in 2050, then, calls for making assumptions about the numbers of people entering and leaving the country, about the numbers from various racial and ethnic groups within the totals, and about the fertility and mortality rates of individual groups. Moreover, it calls for assumptions about exogamy and ethnic affiliation— the degree to which groups intermarry and the way the descendants of intergroup marriages identify themselves.
This chapter offers a view of how future immigration will alter the U.S. population.2 To paint that portrait, a framework is used to ensure consistency for
Even the apparently simple flow of immigrants into the country is not completely straightforward. The relevant concept is net immigration, the difference between the number of those entering the country and the number of those leaving it, whether foreign-born or native-born. These flows respond to various economic, political, social, and family concerns, in the United States as well as in the sending countries, that themselves may be volatile.
The panel is aware that our population projections may be of great interest to those with environmental concerns. Different immigration assumptions, as will be seen, have substantial influence on the future path of population size and growth for the United States. The panel was not charged with examining the environmental repercussions of population change and does not discuss these issues in this report. The panel does not have particular expertise in environmental studies and did not give special study to the effect of immigration on the environment.