International migration also calls for assumptions about the generational composition of migrants. Immigrants to a population are almost exclusively foreign-born.8 Emigrants from the United States are predominantly members of the first generation: people who have emigrated to the United States and then decided to return to their country of birth. A relatively small number of native-born residents, second or later generation, also emigrate from the United States.
The base populations were defined for July 1, 1995, and rely on information from April 1, 1990, the date for the 1990 U.S. Census of Population, and post-census estimates made by the U.S. Bureau of the Census (1996a). The age-sex distributions for the four immigrant generations in each ethnic group were taken from fitted projections of the U.S. population for the years 1880 to 1990. To obtain their numbers by generation, the projections were scaled, by ethnic group, to the 1970 census (for the first, second, and third and later generations) and the 1980 and 1990 censuses (for the native- and foreign-born). Finally, the population figures were scaled to the post-census age-sex distributions for the total population, by ethnic group, estimated by the U.S. Bureau of the Census (1996a).
For this chapter, we include estimates for the 1995 population by single and multiple-ancestry. We consider two types of births in these projections: single-ancestry births are those to parents who have the same racial or ethnic identification; multiple-ancestry births are births to parents whose racial or ethnic identifications differ. Single ancestry, in the context of this chapter, means that a person reports a racial or ethnic ancestry that is the same as his or her primary racial or ethnic identification.
To obtain estimates of single and multiple-ancestry, we used the 1990 census to divide persons in each of the four main racial/ethnic groups into two groups: (1) single-ancestry persons, who reported that both ancestries were the same as their racial/Hispanic-origin identification and (2) multiple-ancestry persons, who reported one or more ancestries that differed from their racial/Hispanic-origin group identification.
Overall, the proportion of multiple-ancestry for the four main racial/ethnic groups varies a lot. About 7 percent of the U.S. population reported multiple-ancestry in the 1990 census. Of those who reported their primary ethnic affiliation as white, about 6 percent reported one or more ancestries that were not white. Of those reporting themselves as black, about 7 percent reported one or more
There are small numbers of immigrants to the United States who are native-born persons with foreign citizenship who immigrate. For example, a foreign-born couple residing in the United States may have children born in the United States and, subsequently, return to the country of their own birth. If their children later return to the United States, they would be immigrants from the second generation.