Before launching into a description of the nine individual categories of international migration, we are providing a definition of international migration that is consistent with the goals of the Census Bureau's Population Estimates Programs.
For purposes of the Census Bureau's population estimates programs, an individual is classified as an International Migrant if his or her crossing of the United States border would necessitate a change in the resident population of the United States as defined in Decennial Census operations.
Tourists (either American or foreign) and "Day Workers" are not international migrants under that definition. But military reservists who served abroad in the Desert Storm Operation would have been treated as international out-migrants when they departed from the United States and international in-migrants when they returned to the United States. American college students who study abroad and foreign students who matriculate at American universities would also be classified as international migrants for Census purposes.
The 9 categories of international migration listed below (see Appendix A) are extremely diverse. The first four entries (1 through 4) satisfy traditional images of international migration and these are the only immigration categories that are used explicitly when generating LOCAL Population Estimates. Migration categories 5 through 8 generally pertain to the international movement of United States citizens. Visitors (Category 9) theoretically have no affect on the decennial census but in practice they probably do.
Nine Categories of International Migration
- Legal Immigrants
- Undocumented Immigrants
- Puerto Rican Migration
- Movement of Armed Forces and their Dependents
- Movement of Civilian Federal Employees and their Dependents
- Movement of non Federal Employees and their Dependents
- Students, temporary workers, and exchange visitors
The National Population Estimates model for calculating net residual migration certainly requires a compilation of categories 1, 2, 3 , and 4; but it also relies on numerical estimates for categories 5 and 6. Since the local estimates program does not explicitly consider persons falling in international migration categories 5 and 6 as immigrants, the sum of the international migration estimates for the individual states will not match the national estimates of net residual migration. (The procedures used in estimating local area migration appears in section 3--Estimating Domestic Migration Flows).
This lack of closure does not appeal to demographers who want population estimation models to follow a strict demographic accounts procedure (as shown in equation 1). Conceptually, it is possible to construct a place specific estimate of international migration for categories 5 and 6. But (1) this component is already subsumed as a domestic migration component--see page 11, (2) these two categories of international migration would be highly concentrated towards areas with large military populations, and (3) there is no explicit information for allocating this component to any individual military base.
Moreover, the migration of persons falling into international migration categories 5 and 6 is largely "temporary". Analysts interested in immigration data would not want estimates of "permanent" immigration contaminated with the inclusion of these two categories.
The measurement of immigration and emigration is much more complicated than the measure of births and deaths. Much of this complication arises because the Census Bureau definitions of the 9 subcategories of immigration and emigration presented do not resemble formal definitions employed by the Immigration and Naturalization Service (INS) nor do they match the working definition set out in bold print on the previous page.
The formal (INS) definition of immigration appears in section 2.1.1. INS does not define emigration because it does not collect statistics on emigration; however, the U.N. recommendation of emigration presupposes intent as well as a time span (one year).
2.1 Direct Migration Flows
The first four categories of international migration are considered to be "direct" because their movement cannot be traced by matching addresses on adjacent IRS returns. Thus it is imperative to design a system for assigning their immigration down to specific States, counties and places.
The administrative data for legal immigration (section 2.1.1 below) are thought to be as reliable as administrative data on births and deaths. Furthermore, legal immigration is numerically (600,000 per year) the most important of the international migration categories. Estimates of the remaining components of immigration require somewhat heroic assumptions which are not always satisfactory.
2.1.1 Category 1, Legal Immigration: INS defines an immigrant to be an alien who has been admitted to the United States for the purpose of legal permanent residence. All immigrants are issued an I-551 document from INS; the I-551 is better known as the Green Card.
Refugees are a specific class of "nonimmigrants" who are generally permitted to adjust to immigrant status at a later date. An immigrant may eventually become a citizen; but lack of citizenship does not cause a resident to be excluded from enumeration in a United States Decennial Census.
INS maintains exceedingly detailed data sets for persons meeting their definitions of an immigrant (see Immigration and Naturalization Service, 1991). The administrative numbers (approximately 600,000 per annum) from INS are assignable to specific geographic entries within the United States.
2.1.2 Category 2, Undocumented Immigration: This component consists of aliens who do not have legal status in the United States; yet who are enumerated in a United States Census. The Decennial Census questionnaire is not constructed to determine legal status, and there are no explicit steps taken to exclude this group from the enumeration process. The majority of the undocumented immigration in this country are thought to arrive from Mexico and Central America. Moreover, a disproportionate share of the Hispanic undocumented population settles in California.
There are no regular administrative data sources for determining a precise number of undocumented residents in the United States. However, several coordinated research activities lead us to believe that this population is increasing by approximately 200,000 per year (see Passel and Woodrow, 1984).
We obtained the 200,000 figure cited above in several steps. First the 1980 Census count of recent (1975 to 1980) foreign born arrivals is assumed to be the sum of legal and undocumented immigrants arriving in this country over that time interval. In comparing 1980 Census figures of the foreign born who settled in this country after 1975 to INS sources of the "legally" resident foreign born who entered the United States between 1975 and 1980, it is "apparent" that nearly 1,000,000 net undocumented immigrants who entered this country between 1975 and 1980 were enumerated in the 1980 Census (see Warren and Passel 1987). The Census sample is sufficiently large to partition this total estimate of undocumented immigrants to individual countries. By this operation, we estimate that 60 percent of the recent arriving undocumented aliens come from Mexico. Column 5 of table 1 contains more specific information.
Concurrent analyses from Current Population Survey (CPS) data for the 1979-83 period also supported an estimate of 200,000 total illegal immigrants per annum; but that sample is not large enough to produce an independent estimate of undocumented immigrants by source country. If subsequent surveys had indicated that the original 200,000 estimate was no longer viable, we would have considered making a change to this component for the later years of the 1980 decade; but subsequent analyses of CPS data for 1986, 1988, and 1989 indicated that there was no evidence to support a change on the original 200,000 estimate (see Passel, 1986, for discussion surrounding the inclusion of the 200,000 figure for purposes of producing population estimates during the 1980's; and see Woodrow, 1991, for a review of the CPS estimates of the undocumented population).
The method for developing estimates of this enumerated undocumented population entering the United States between 1975 and 1980 relies heavily on independent estimates of emigration (described next) who left the United States in the same 1975-80 period.
2.1.3 Category 3, Emigration: Emigration is the process whereby a legal resident of the United States leaves this country and takes up permanent residence in a foreign nation. There are no current programmatic reasons for the United States Government to record emigration data, and the Government abandoned any pretext of collecting that data in 1957. It is necessary, however, to establish a numerical value for this component in a population estimates model.
Emigration estimates are constructed from the same analytical processes used in estimating the flow of undocumented aliens into the United States. Briefly, empirically based estimates of emigration were developed for the 1960-70 decade from a cohort analysis of 1960 and 1970 census data on the foreign born population (see Warren and Peck, 1980); a second set of estimates were developed from a systematic analysis of how the INS series of total alien registrants was affected via annual INS data on intended legal residents (see Warren and Kraley, 1985).
Both of these procedures suggest that the level of emigration for the 1975-80 period was close to 160,000 per year. For purposes of population estimation, we have assumed that emigration continued at that level throughout the 1980's. From the data appearing in columns 5 and 6 of table 1, one will note a striking difference between the countries favored by emigrants as opposed to the source country(s) of the incoming undocumented population.
For purposes of population estimates, we subdivide emigrants into two classes: native born emigrants and emigrants who were born abroad. We estimate the level of all emigrants to be 160,000 per year. It is assumed that 27,000 of these emigrants are native born while the remaining 133,000 are foreign born.
Conceivably one might wonder about the magnitude of the group--"emigrating" illegal aliens. The restricted definition of an emigrant (the exit of a legal resident of the United States) renders this concept moot. The estimate of undocumented immigration--200,000 per year (discussed in section 2.1.2) is a net measure that makes no explicit allowance for the departure of undocumented residents.
In the near future, we will be examining 1990 Census and Current Population Survey (CPS) results in conjunction with recent INS statistics in order to update the existing estimates of net undocumented immigration (200,000) as well as the current annual estimates of emigration (160,000). All tables included at the back of this paper were prepared using 1980 data based estimates.
2.1.4 Category 4, Puerto Rican Migration: Because Puerto Rico is a Commonwealth of the United States and its residents are citizens of the United States, there is no restriction on movement between the United States and Puerto Rico. However, the methodology used in estimating the resident population of the United States does require that we differentiate the population of Puerto Rico from that of the mainland United States. For lack of any better data, the calculation of movement between Puerto Rico and the United States mainland is derived from "differencing" airline passenger data into and out of the San Juan airport.
This differencing procedure ostensibly enables us to separate tourists, who number in the millions from immigrants/emigrants who number in the thousands. However, the amount of error in the 1990 population estimate of the Commonwealth of Puerto Rico vis a vis its 1990 Census count is approximately 200,000 or about 6 percent of Puerto Rico's population. An error of this magnitude demonstrates that the passenger data is not an acceptable source for estimating migration between Puerto Rico and the mainland United States.
Based on the passenger data series, the estimated level of annual "net" movement between Puerto Rico and the mainland of the United States has been as high as 40,000 in either direction. Although 40,000 is not a large component in terms of United States population change, it takes on added importance because the "permanent" migration to and from Puerto Rico is considered to be entirely Hispanic. Moreover, Puerto Rican migration is almost entirely limited to the East Coast of the United States.
Theoretically, we should treat Guam, American Samoa, the Virgin Islands and any other Trust Territory in a manner analogous to Puerto Rico. As a practical matter, the numbers involved are so small and the potential effect on the U.S. population is so slight, that these remaining outlying area flows are ignored in the population estimates model.
2.2 Abstract Migration Flows:
Unlike the "direct" migration flows discussed in section 2.1, international migration categories 5 through 9 (below) deal with a concept of an "abstract net migration flow" as opposed to explicit data on individual movement across the boundaries of the United States. The calculations of these abstract net migration flows are determined by performing successive subtractions on annual stock (or group) data.
2.2.1 Category 5, Armed Forces: Armed Forces personnel serving overseas would not normally be enumerated in a decennial census. Throughout the 1980's, the size of the overseas Armed Forces population hovered around 500,000. In March, 1991, our nation's participation in Desert Storm caused the overseas Armed Forces population to soar to 700,000. But by the middle of 1992 the overseas military population had dipped below 400,000. Thus in the space of only two years, the United States had an Armed Forces out-migration of 200,000 which was then countered by an in-migration of 300,000.
Administrative counts of the overseas military population are furnished on a monthly basis by the Department of Defense (DOD). In addition to these monthly estimates of the overseas military population, (DOD) also provides data relating to the size of the overseas Armed Forces Dependent population.
The administrative counts of the overseas Armed Forces and their dependents, along with the administrative counts of the overseas civilian Federal employees (Category 7, section 2.2.3) and their dependents as of April 1, 1990 were appended to the 1990 resident Census for computing the apportionment population. The total supplementary overseas population on April 1, 1990 was 922,819.
2.2.2 Category 6, Civilian Federal Employees: The Office of Personnel Management (OPM) supplies monthly data on the number of Civilian Federal Employees who are working overseas at any time. That number is relatively constant and at this time (1992) is about 60,000. For purposes of population estimation we assume that each federal overseas employee has on average 1.2 dependents.
2.2.3 Category 7, Non Federal Employees: There are no reliable data on the number of non federal employees and/or their dependents who are overseas at any point in time. These persons would not normally be expected to be enumerated in a decennial census. The size of this population (like students--category 8 in section 2.2.4 below) would only affect the size of the United States resident population if it were subject to large fluctuations.
2.2.4 Category 8, Students, Temporary Workers, and Exchange Visitors: Persons fitting this category are not strictly defined as immigrants because they do not have immigrant status (see international migration category 1 in section 2.1.1). But citizens of foreign countries residing in the United States with these qualifications would normally be enumerated in a decennial census at their American address. Likewise, American students who are studying abroad at Census time should not be included in our census.
It is certainly possible to tabulate the number of foreign students by location within this country at the time of our decennial census; but the decennial census provides no information on the numbers of American students who are studying abroad. The Census Bureau does not estimate the numbers of foreign students in this country or American students overseas on an ongoing basis. However, an annual survey conducted by the Institute of International Education indicates that there were (in 1991) approximately 400,000 foreign students in the United States as opposed to 75,000 Amercians who are studying abroad. 50 percent of the foreign students are citizens of various Asian countries.
In terms of the postcensal estimates program, it is not critical to have a "fix" on the size of either student group provided that the numbers (race/origin/age/sex) are relatively constant over time.
2.2.5 Category 9, Visitors: Visitors from foreign nations are not supposed to be enumerated in the United States Decennial Census, and Americans who are temporarily in another country on Census Day will be enumerated at their usual place of residence within the United States (see 1990 Census of Population and Housing, 1991). We make no attempt at estimating the size of either group because it has no effect on a population estimate.
In practice, the visitor from overseas who stays only in commercial establishments would have little opportunity to be erroneously enumerated in our Census. However, if the "visit" is one of long duration to a housing unit, the visitor might well be enumerated in our Census. By the same token, an American resident who is between residences and who is on an extended visit overseas might not be enumerated in our Decennial Census.