alternative assumptions about the future course of immigration and emigration and their associated demographic implications. This work has several purposes:
On the basis of our population projection model, this chapter examines the effects of immigration on the future course of the U.S. population. We first examine why immigration is important for population change. Next, a model for population projection is briefly described, and the alternative assumptions used here to illustrate future population change are set out. Against this background, the heart of the chapter is a discussion of the main effects of immigration on the U.S. population over the next six decades.
The number and age structure of the population are determined by fertility, mortality, and migration. The last factor has attracted considerably less attention in formal models than the first two, which have been extensively examined by means of stable population models and their various extensions.
At the simplest level, that of total population numbers, only net migration appears in the demographic balancing equation: population change = births deaths + net migration. Thus, net migration series are typically used to examine the effects of immigration on population structure. For most of its history, the United States has attracted large numbers of immigrants. In recent years, the estimated net inflow has been around 800,000 people, including illegal and legal immigrants and refugees. This figure reflects immigrant flows into the country and emigrant departures of both immigrants and native-born residents. Although the net figure is important from the demographic accounting perspective, gross inflows and outflows are necessary for many purposes of policy and analysis. To cite one example: immigrants who are not U.S. citizens are ineligible to vote, but emigrants who are U.S. citizens are eligible to vote by absentee ballot.
The world population has been growing at a historically unprecedented rate