U.S. Census Bureau Measurement of Net International

Migration to the United States:

1990 to 2000

Population Division Working Paper No. 51

 Tammany J. Mulder

Frederick W. Hollmann

 Lisa R. Lollock

 Rachel C. Cassidy

 Joseph M. Costanzo

 and Josephine D. Baker

 Population Division

 U.S. Census Bureau

 Department of Commerce

 Washington, D.C. 20233

 (301) 457-2428

 www.census.gov

December 2001
U.S. Census Bureau

1

 

ABSTRACT

The U.S. Census Bureau produces national population estimates on an annual basis using

methodology that incorporates the three main determinants of population change: births, deaths,

and net migration. Net international migration plays an integral role in determining both the size

and demographic composition of the population at the national level. It is the most complex

determinant of population change, and its complete measurement involves the measurement of

several sub-components, each one using separate methodology. In view of the fact that these

sub-components are estimated separately, each is subject to differing levels of uncertainty or

bias. This paper provides a detailed discussion of the definitions, methodologies, assumptions,

and data sources used to measure net international migration, including a brief description of

estimates for geography and demographic characteristics. Following the discussion of the subcomponents of net international migration, the strengths and limitations of each are presented

along with potential research and developments.

ACKNOWLEDGEMENTS

This report was prepared under the general direction of Bashir Ahmed, Chief of the

Administrative Records and Methodology Research Branch. Signe Wetrogan, Assistant Division

Chief for Population Estimates and Projections, provided overall direction. Professional

consultation was provided by Robert Warren, J. Gregory Robinson, Kevin Deardorff, Gregory

Spencer, Todd Gardner, David Word, and Frank Hobbs.

* This paper reports the results of research and analysis undertaken by Census Bureau staff. It

has undergone a more limited review than official Census Bureau publications. This report is

released to inform interested parties of research and to encourage discussion.
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TABLE OF CONTENTS

I. Introduction

Post-censal national population estimates

Net international migration to the United States

II. Major Sub-Components of Net International Migration

Legal Immigration

Data sources

Methodology

Strengths and limitations

Migration of refugees

Data sources

Methodology

Strengths and limitations

Net unauthorized migration to the United States

Data sources

Methodology

Strengths and limitations

Emigration

Data sources

Methodology: emigration of U.S. natives

Methodology: emigration of foreign-born legal residents

Strengths and limitations

Net migration from Puerto Rico

Data and methodology

Strengths and limitations

Net temporary migration

Methodology: net temporary migration

Methodology: net specialty workers

Strengths and limitations

III. Conclusion

IV. Tables and Appendices

Table 1. The total resident population and net international migration component for the vintage 2000

post-censal national estimates: 1990 to 2000.

Table 2. Net international migration and its sub-components for the vintage 2000 post-censal national

estimates: 1990 to 2000.

Table 3. Distribution of legal immigration by major class of admission from the Immigration and

Naturalization Service: fiscal year 1998.

Table 4. Net international migration and legal immigration numeric change, percent change, and crude

net legal immigration rate for the vintage 2000 post-censal national estimates: 1990 to 2000.

Table 5. Legal immigrants by country of birth categories for the federal fiscal year ending September

30, as applied to the vintage 2000 post-censal national estimates: 1990 to 1999.

Table 6. Alternative estimates of annual net additions of the unauthorized migrant population,

analyzed in selecting the estimate of 225,000 per year.

Table 7. Emigrants by nativity for the vintage 2000 post-censal national estimates: 1990 to 2000.

Table 8. Nonimmigrants by special worker H-1B status for the vintage 2000 post-censal national

estimates: 1990 to 2000.

Appendix A. Identification of nonimmigrants for the 1990 census.
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I. INTRODUCTION

The U.S. Census Bureau produces national population estimates on an annual basis using

methodology that incorporates the three main determinants of population change: births, deaths,

and net migration. Net international migration plays an integral role in determining both the size

and demographic composition of the population at the national level. It is the most complex

determinant of population change, and its complete measurement involves the measurement of

several sub-components, each one using separate methodology. In view of the fact that these

sub-components are estimated separately, each is subject to differing levels of uncertainty or

bias. This paper provides a detailed discussion of the definitions, methodologies, assumptions,

and data sources used to measure net international migration, including a brief description of

estimates for geography and demographic characteristics. Following the discussion of the subcomponents of net international migration, the strengths and limitations of each are presented

along with potential research and developments.1

Post-censal national population estimates

The U.S. Census Bureau produces national population estimates for the resident population of

the United States by single year of age, sex, race, Hispanic origin, and nativity.2 These estimates

are developed using the component method, described by the “balancing equation” (Equation 1).

This method accounts for the change in national population trends derived from the three major

components of population change: births, deaths, and net migration. The estimate series begins

with a base population derived primarily from decennial census results, and is updated each year

using the most recent administrative data available on births, deaths, and net migration. Because

new data continue to become available and revisions are made to historical series, each new

annual series requires the development of the estimates from census date forward to the new

estimate date.3 Therefore, the series produced each year reflects demographic change

experienced throughout the decade using the most recent data available. The estimates also

account for the movement of the Armed Forces overseas and civilian citizens to the United

States, which are included separately from the net international migration component.

 

1

 This paper reflects updated research of net international migration at the national level reported by Word (1992)

in “The Census Bureau Approach for Allocating International Migration to States, Counties and Places: 1981-1991,”

Population Estimates and Projections Technical Working Paper No. 1.

2

 The resident population includes people who reside in the 50 states and the District of Columbia. It excludes

residents of the Commonwealth of Puerto Rico, and residents of outlying areas under United States sovereignty or

jurisdiction (principally American Samoa, Guam, U.S. Virgin Islands, and the Commonwealth of the Northern

Mariana Islands). The estimates exclude the United States Armed Forces overseas, as well as civilian United States

citizens whose usual residence is outside the United States. The foreign-born population is designated by the

absence of United States citizenship at birth and includes naturalized citizens and non-citizens residing in the United

States. Consequently, a person is considered "native" if he or she is born in the United States or is born abroad to at

least one parent with U.S. citizenship.

3

 Hereafter, these revisions are referred to as a “vintage.” For example, “vintage 2000 estimates” refers to the

revision produced in the year 2000.
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Equation 1. Pt = P t-1 + B t-1,t – D t-1,t + NIM t-1,t + NCM t-1,t (1)

where

Pt = population at time t;

P t-1 = population at time t-1;

B t-1,t = births, in the interval from time t-1 to time t;

D t-1,t = deaths, in the interval from time t-1 to time t;

NIM t-1,t = net international migration, in the interval from time t-1 to time t; and

NCM t-1,t = net movement of U.S. Armed Forces and civilian citizens to the United States.

Once the base population (Pt-1) for estimates is established for April 1 of the decennial year,

estimates for future designated time intervals (Pt) are made by adding the number of

births (Bt-1,t), subtracting the number of deaths (D t-1,t), and adding estimates of the two net

migration components shown in Equation 1 to the census base population. Administrative data

on births and deaths for U.S. residents are tabulated by the National Center for Health Statistics

(NCHS). Data on net international migration are primarily collected by the Immigration and

Naturalization Service (INS). The INS data, along with other administrative sources, will be

discussed in detail below.

Table 1 presents the latest estimates for the total resident population and the net international

migration component (vintage 2000).4 Throughout the decade, the population increased from

248.8 million as of April 1, 1990, to 274.6 million as of April 1, 2000, an increase of 25.8

million people, or 9.4 percent.5

Net international migration to the United States

Migration is typically defined as a permanent geographic or spatial change in usual residence

from one defined area to another. International migration consists of people changing permanent

residence across national boundaries. U.S. immigration law defines immigration as the

acquisition of legal permanent residence in the United States by non-citizens. In reference to the

national estimates, net international migration to the United States is the net of 1) migration to

the United States and 2) permanent departure from the United States. Currently, this component

is construed to also include net migration from Puerto Rico and the movement of the

unauthorized population. Temporary international movement of U.S. citizens, including the

Armed Forces and their dependents, is not included in net international migration and is treated

separately, as shown in Equation 1.

Among the 25.8 million people added to the total U.S. population throughout the decade, more

than 8 million were estimated to be added as a result of the net international migration

component (Table 1). The amount of net international migration generally increased throughout

the decade, from 699,000 in 1990-91 to 931,000 in 1996-97. After 1997, net international

migration remained relatively stable between 884,000 for 1997-98 and 863,000 for 1998-99.

 

4

 The estimates, referred to as vintage 2000 estimates, were prepared for evaluation of Census 2000.

5

 Hereafter, year refers to the year ending June 30, which begins on July 1 of the previous year.
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For the purposes of the national estimates, net international migration is divided into several subcomponents (Equation 2): 1) legal immigration; 2) movement of refugees; 3) net unauthorized

migration; 4) emigration; 5) net temporary migration; and 6) net migration from Puerto Rico.

Equation 2. NIM t-1,t = LPR t-1,t + RE t-1,t – E t-1,t + NU t-1,t + NT t-1,t + NPR t-1,t (2)

where

LPR t-1,t = legal immigration, in the interval from time t-1 to time t;

RE t-1,t = movement of refugees from time t-1 to time t;

E t-1,t = emigration of legal residents from time t-1 to time t;

NU t-1,t = net unauthorized migration from time t-1 to time t;

NT t-1,t = net temporary migration from time t-1 to time t; and

NPR t-1,t = net migration from Puerto Rico from time t-1 to time t.

Table 2 displays the estimates used for each sub-component from 1990 to 2000 for the national

estimates produced in 2000, referred to as vintage 2000. Legal immigration (LPR), the largest

contributing sub-component to net international migration, refers to immigrants admitted to the

United States for legal permanent residence, as defined by INS (INS 2000). Under the

Immigration Act of 1990, immigrants entering as legal immigrants are admitted under several

categories of admission including family sponsorship (close relatives of U.S. citizens or legal

permanent residents) and employment preference, among others. Throughout the decade, the

number of legal immigrants added annually ranged from 577,000 migrants in 1990-91 to

883,000 migrants in 1996-97 (Table 2).

The second largest contributing sub-component, net unauthorized migration (NU) is an estimate

of the annual addition of migrants residing in the United States without legal status net of

mortality and emigration. Unauthorized migrants include those who entered the United States

without prior authorization and those who violated the terms of or overstayed a temporary

(nonimmigrant) visa. The estimates for this population are produced using indirect methods and

are currently assumed to be a constant net annual addition of 225,000 migrants each year.

Refugees (RE) are defined as those people outside their country of nationality who are unable or

unwilling to return to that country because of persecution or a well-founded fear of persecution,

which coincides with the definition determined by the 1967 United Nations Protocol on

Refugees (United Nations 2000). The estimated number of refugees is based on data provided

by the Office of Refugee Resettlement (ORR) of the Department of Health and Human Services

(DHHS), and fluctuates each year depending on the occurrence of foreign political upheavals and

U.S. policy with respect to their victims. For the 1990-2000 decade, the number of refugees

added annually ranged between a low of 78,000 in 1997-98 and a high of 128,000 for 1994-95.

The Census Bureau also makes an allowance for the net movement from Puerto Rico (NPR) to

the United States. This allowance is based on trends during the 1980s, and is assumed to be a

constant net annual addition to the United States of 12,646 migrants each year for the 1990-2000

decade.

Net temporary migration (NT), also known as “nonimmigrants,” represents migrants legally

admitted into the United States on a temporary visa, who reside in the United States for a

specified period of time. Theoretically, this population includes temporary visitors for business

and/or pleasure, foreign government officials, treaty officials, foreign and exchange students,
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temporary workers, and religious workers, among others.6 Some classifications of this

movement are estimated by indirect means; either from supplementary data sources or by

assuming the number of such people residing in the United States remains constant over time.

Throughout the 1990-2000 decade, the number of nonimmigrants added annually ranged from

669 migrants (multiple years) to 72,000 for 1998-99.

Particular sub-components discussed above are migratory flows in a single direction (“in” or

“out”), while others represent net flows, or the difference of “in” minus “out.” Emigration (E),

defined as the permanent departure from a country of residence, is the one-way flow of United

States permanent residents leaving the United States to reside abroad differentiated by nativity

status. This definition excludes the departure of unauthorized migrants, migrants to Puerto Rico,

and nonimmigrants, as their respective sub-components are already estimated net of emigration.

The estimated number of annual emigrants for the 1990-2000 decade increased from 252,000

migrants in 1990-91 to 279,000 migrants in 1998-99.

Net international migration to the United States is the sum of these independently derived subcomponents (Equation 2). The estimation of net international migration to the United States,

therefore, is not simply the tabulation of gross immigration to and gross emigration from the

United States. Because some of the sub-components are estimates of net migration and are not

estimated as separate flow measures in or out of the United States, we are unable to distinguish

the gross movement of each group. Estimates of each sub-component require the use of different

data sources and both direct and indirect estimation techniques, resulting in differing levels of

data quality. Depending on the source, data are collected at different points throughout the year

or on an annual basis. In addition, the determinants for each sub-component are diverse.

Consequently, net international migration to the United States represents the most difficult and

problematic component of demographic change to estimate. The following sections discuss each

sub-component of net international migration, review the strengths and limitations of their

measurement, and present potential research and developments.

II. MAJOR SUB-COMPONENTS OF NET INTERNATIONAL MIGRATION

Legal immigration

The sub-component of net international migration, legal immigration (LPR), refers to noncitizens who are granted legal permanent residence in the United States by the federal

government, or who reside in the United States and will ultimately be granted this status. Legal

permanent residence includes the right to remain in the country indefinitely, to be gainfully

employed, and to seek the benefits of U.S. citizenship through naturalization.

The character of legal immigration is highly dependent on current immigration law. Major

revisions of the U.S. immigration code include the Immigration and Nationality Act

 

6

 For the purposes of population estimates, temporary visitors for business and pleasure are not considered

residents, and therefore are not included in this sub-component.
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Amendments of 1965. Under this Act, numerical limitations were placed on various categories

of immigration. Moreover, the Act was groundbreaking in the sense that it defined one class of

immigrants--immediate relatives of U.S. citizens--that was not subject to a numerical limitation.

A major overhaul of the Act in 1990 established a special class of immigrants known as

“diversity immigrants” who are chosen by lottery from countries that have a history of being

underrepresented among immigrants. Finally, the Act established a set of “preferences,” or

priorities, among other family-sponsored immigrants (besides immediate relatives of citizens)

and employment-based immigrants, with an elaborate formula by which numerical limitations

were imposed on the resulting preference groups. Table 3 summarizes the distribution of the

major legal immigrant categories and identifies whether they are subject to numerical limitations.

The majority of legal immigrants granted permanent residence in FY1998 were immediate

relatives of U.S. citizens, followed by family sponsorship preference migrants and employment

preference migrants.

Legal immigrants obtain permanent resident status through two separate mechanisms that do not

differ in legal requirements, depending on where they live at the time of application. The INS

accepts the applications for permanent resident status for people living in the United States when

they apply. Referred to as adjustees, this category generally consists of, but is not limited to,

nonimmigrants, refugees, asylees (people granted political asylum), and unauthorized residents.

In contrast, the U.S. Department of State (DOS) accepts applications and issues visas from

consular offices abroad to potential immigrants residing outside the United States, which are

processed as they enter the United States. These immigrants are referred to as new arrivals.

Consequently, applicants can obtain permanent residence in the United States with or without

changing geographic residence before immigration. In fact, immigrants may be living in the

United States for a number of years while awaiting adjustment to immigrant status. During this

time, they are likely to view themselves as U.S. residents, and are therefore in the U.S.

population for the purposes of population estimates. As of 1995, the number of adjustees and

new arrivals remained about equal in proportion, with adjustees generally outnumbering new

arrivals each year.

In preparing estimates of the legal immigrant sub-component of international migration, we treat

new arrivals and adjustees differently, although both are sizeable contributors to this category.

The treatment of new arrivals is relatively simple because their month and year of admission, as

well as various demographic characteristics (age, sex, country of birth, location of intended

residence) are indicated in the INS immigrant data, and can be assumed to apply as of the time of

their entry into the United States. For adjustees, the situation is more complex. Because

adjustees arrive in the United States prior to being granted legal permanent residence, their date

of admission does not define when they came to live in the United States. For some classes

(refugees and some asylees), the time series of actual arrivals can be determined more effectively

from non-INS data sources (see the Migration of refugees section). The methodology for the

inclusion of adjustees, both with respect to the timing of their arrival and assignment of

characteristics, is discussed below. International migration of legal immigrants in a given time

period consists of the following:

1) “New arrival” immigrants with date of admission in the given time period.
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2) An estimate of nonimmigrant entries, derived from the number of adjustees and

adjustee applicants in the given time period, but excluding the following:

a) Refugees and some Cuban and Haitian asylees, whose records must be excluded

from the INS data. These are included as a separate sub-component

(see the Migration of refugees section).

b) Legal temporary residents who will not become legal permanent residents. These

are included as a separate sub-component (see the Net temporary migration

section).

c) Unauthorized migrants who will not become legal permanent residents. These are

included as a separate sub-component (see the Net unauthorized migration to the

United States section).

d) A small number of people admitted under special, “one-time” laws who also have

a nonimmigrant arrival date before the 1990 census. These people should neither

be included for themselves (given that they could be included in the base

population) nor serve as proxies for other groups (because of the circumstances of

their admission).

Legal immigration accounts for the largest contribution to the annual addition of net international

migrants. As shown in Table 4, throughout the decade, legal immigration comprised more than

80 percent of the net international migration component each year, adding more than 7 million

legal residents. The number of legal immigrants can fluctuate from year to year, irrespective of

the numeric limits determined by government policy. The number of legal immigrants granted

permanent status increased early in the decade with the exception of a decline in 1993-1994.

Following 1995, the number and growth rate for legal immigrants declined. As displayed by the

numeric and percent change for the decade, the number of legal immigrants admitted by the INS

and the Department of State combined has declined consistently since 1996-1997.

A likely factor in both the increase and decline of legal immigration during the 1990-2000

decade has been the secondary effect of the Immigration Reform and Control Act (IRCA) of

1986. This law granted amnesty to a large class of unauthorized residents in 1987 and 1988,

allowing them to remain in the country, later seek legal permanent residence, and ultimately

obtain U.S. citizenship. IRCA beneficiaries, in turn, could sponsor immediate relatives who

were then granted legal permanent residence. For sponsors who were legally resident noncitizens, the number of secondary immigrants was numerically limited; however, for U.S. citizen

sponsors, the number of immediate relatives was unlimited. This may have partly explained the

increase in legal immigration during the early 1990s. In the later years of the decade, a slowdown in the processing of adjustee applications meant that many immigrants who applied under

these provisions had their processing delayed. In addition, the supply of potential immigrants

may have been partially absorbed, given the limitation in the number of potential sponsors. This

could provide an explanation for some of the decline in legal immigration that occurred.

Data sources

Legal immigrants are estimated annually by single year of age, sex, race, Hispanic origin, and

county of intended residence in the United States. County of intended residence is estimated

from the zip code of intended residence to a respective county. The county level data are then

aggregated to estimate the total number of legal immigrants at the state and national level. The
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numbers of legal immigrants are estimated by month of admission and are projected beyond the

last available fiscal year of INS data, generally ending in September prior to the year the

estimates are produced.

Estimation of legal immigration is dependent on microdata on legal immigrants supplied by the

INS. The INS provides the Census Bureau annually with a file containing non-identifiable

individual records of legal immigrants admitted during the federal fiscal year of October 1 to

September 30. Variables included in the data set pertain to time of admission, class of admission

(identifying the law under which the immigrant was admitted and whether the immigrant is a

new arrival or adjustee), demographic characteristics, and intended residence. The following are

the primary variables available on the INS microdata file that are used to produce the estimated

legal immigrant detail:

a. month of admission

b. year of admission

c. class of admission7

d. country of birth

e. sex

f. age

g. zip code of intended residence

h. nonimmigrant year of arrival (adjustees only)

The data set does not include information on any personal identifiers including race and Hispanic

origin.

To supplement the microdata file, the INS also provides provisional data on the number of

adjustee applicants by fiscal year. In addition to INS data, the Census Bureau utilizes an internal

data set providing information on geographic identification of zip codes and decennial census

data on race and Hispanic origin of the foreign-born population by country of birth.

Methodology

There are a number of steps involved in converting the INS immigrant microdata file to the

estimates of legal immigration used for the population estimates program, including geographic

and demographic detail. The steps are summarized below:

1) Distinguishing arrivals from adjustees: Class of admission is a coding of the legal

provision under which an immigrant is admitted, and is used to identify how each case is to be

included in the accounting of population change. Most importantly, this variable distinguishes

new arrivals from “adjustees” who previously resided in the United States in a nonimmigrant

legal status. Within the category of adjustees, class of admission indicates which immigrants

previously entered as refugees, to be included from another data source (hence discounted at this

point), and which ones must be used as “proxies” for nonimmigrants not counted elsewhere who

 

7

 Microdata files provided by the INS did not include immigrants granted legal permanent residence from 1990-

2000 under the Immigration Reform and Control Act (IRCA) of 1986. Eligibility for legal permanent residence

under IRCA pertained to those illegally present or working in the United States between 1982 and 1986. Therefore,

in theory these immigrants were enumerated in the 1990 census as criteria
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will become immigrants at a later time. Because immigration law changes from year to year and

class-of-admission coding changes, its interpretation is updated accordingly.

2) Estimating county of intended residence: Zip code of intended residence (a postal

designation) is used to impute political geography, including state and county of residence. This

is somewhat problematic, because zip codes are defined to further the delivery of mail, and tend

to relate more to the location of branch post offices and mail processing centers, and bear no

necessary relationship to local political boundaries. Developed by the Census Bureau in

cooperation with the U.S. Postal Service, the tool used to complete this task is an electronic

catalog that identifies a “dominant” county for each zip code (Sater 1994). For the small number

of cases where the zip code is either not provided or is not valid, we impute the state and county

from known cases with known geography with the same country of birth.

3) Estimating the age and sex composition: Age and sex are included on the INS microdata

file. For small numbers of cases, sex is imputed because it is missing on the file. Imputation is

done using cases where sex is known for the same country of birth. Similarly, age at time of

admission to immigrant status is imputed for a small number of cases for whom it is not coded in

the file, using the age composition of known-age cases of the same sex and country of birth. For

adjustees (even those not included in the accounting at this stage), we must estimate the age at

entry into the United States. This is done using age at adjustment to immigrant status and year of

nonimmigrant arrival. This procedure is complicated somewhat because nonimmigrant year of

arrival is stated in calendar year, with no information on month. Year of nonimmigrant arrival

must be allocated for some cases where it is not coded.

4) Estimating race and Hispanic origin: Race and Hispanic origin of immigrants are imputed

from country of birth. This is done by proration, based on a cross-classification of country of

birth by sex by race by Hispanic origin from 1990 census data. Immigrants of a given country of

birth and sex are assumed to have the same composition by race and Hispanic origin as the

foreign-born population of the same country of birth and sex enumerated in the 1990 census, and

who arrived during the 1985 to 1990 period. This assumption is strong for the vast majority of

countries of birth where the race and Hispanic origin composition is homogeneous; so large

proportions of the population are of a single group (e.g., Hispanic for Latin American countries

and Spain, non-Hispanic Asian and Pacific Islander for East- and South-Asian countries, nonHispanic Black for some Caribbean countries, non-Hispanic white for Europe). A notable

exception is Canada, which supplies a substantial number of immigrants who are racially

diverse. For each country of birth, the distribution by race is assumed to remain constant over

time.

5) Accounting for adjustee “backlog”: For some years, delays in INS processing of adjustee

applications resulted in a large number of accepted adjustee applicants that had not become legal

permanent residents. Under these circumstances, it is more logical to base the series of entries

on the number of applications, rather than the number of those granted legal permanent

residence. For fiscal years 1995 and later, an adjustment must be made for the effects of the

application backlog at INS. This problem affects only the class of migrants estimated to be

arriving based on the number of current adjustees from nonimmigrant to legal immigrant status.

This group, however, may comprise a quarter to a third of the immigrants included in the
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population accounting. We assume that the time series of adjustees (other than refugees) serves

as a proxy for the time series of arriving legal nonimmigrants who will later become legal

immigrants. We base this series on the number submitting applications to the INS as opposed to

the number of applications that INS successfully processes. Until fiscal 1994, there was little

distinction between the two. Beginning in fiscal 1995, a change in immigration law greatly

increased the number of immigration applications that had to be processed by INS (as opposed to

the Department of State), rendering the INS unable to keep up with the number of adjustee

applications. To make allowance for this, adjustee cases from later years were “moved”

backward in time, so that the number of adjustees included from a given year matched the

number of applications–making allowance for applications denied, or cases where successful

applicants decided not to adjust status. We used the class of admission variable to ensure that no

such “moves” would result in exceeding a numerical limit for any admission category. When the

supply of adjustees from later years’ data was exhausted, we replicated cases from existing data

files, reasoning that current successful applicants who would be adjusted in a later year had

characteristics similar to those who had been adjusted already. This process had the effect of

substantially increasing immigration for years where there was an excess of applications over

adjustments, and reducing it somewhat for one–FY 1996–where the backlog from the previous

year was partially absorbed by an excess of adjustments over applications.

6) Identifying year of arrival for “one-time” admission laws: A small number of immigrant

adjustees in the file were admitted under special legal provisions, and would therefore not

represent valid proxies for currently entering nonimmigrants who will adjust status later. These

immigrants are included in principle, but as of their date of arrival, rather than their date of

immigration provided that the latter falls after the 1990 census. An example of this situation is

an employment immigration provision known as the Chinese Students’ Protection Act, which

allowed people born in China to adjust to legal immigrant status as a result of the Tiananmen

Square incident in Beijing.

7) Projecting immigration to last estimate date: In view of the fact that the last available

fiscal year of immigrant data ends with September 30 of the year prior to the July 1 population

estimates date, a short-term projection is necessary to extend the immigration series to the

terminal date of the estimates series. Generally, this projection covers a minimum of nine

months. The projection was confined to immigrants actually included in the population

accounting (e.g., refugees were excluded). During the late 1990s, we simply assume the number

of immigrants in each month matches the number of immigrants 12 months earlier. The

distribution by country of birth is assumed to match that of the last year for which data are

available. Once having established country of birth, the imputation of the other demographic

characteristics and geography as of time of arrival follows the logic used to impute missing

values of characteristics within the data series.

8) Preparing tabular inputs to population estimates: As a final step in the process, the

modified microdata are tabulated to yield the annual number of legal immigrants. Microdata are

converted to tabular files for use in population estimates at the national and sub-national level.

Hence, refugees and other immigrants not included in this step are excluded from the tables and

are retained in a separate file. This file is used to impute characteristics to population totals

derived from other sources, to be described in the sections that follow.
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Strengths and limitations

As is the case with most administrative data, immigration data are collected and maintained to

account for a legal process, rather than to measure population change. We assume the linkage

between future immigrants entering the country as nonimmigrants, and current immigrants who

entered in the past as nonimmigrants is extremely tenuous. While our methodology of adjusting

the immigrant series to account for a backlog in the processing of adjustee applications may

address the issue, it can only address one part of it. We must assume adjustee applications

themselves follow the trend in the nonimmigrant entry of future immigrants.

A high priority for continuing research in the area of legal immigration is to reevaluate the

measurement of nonimmigrants that eventually become legal immigrants. One alternative

method would be to tag all such entries into the country by their nonimmigrant year of arrival

(with possible allowance for multiple arrivals), and then create a projection for those who have

not yet arrived–rather than relying on the “proxy rule” that is currently used. This would have

the advantage of being more accurate on an immigrant-by-immigrant basis. The difficulty would

arise in the determination of a projection for those not yet arrived. Unfortunately, the existing

procedure has been developed incrementally. It might indeed have been optimal before the

adjustee application backlog occurred. When the backlog emerged as an issue, the solution at

hand was to address that issue directly rather than to rethink the entire method by which this

group is estimated. After several years of persistent backlog, the inadequacies of the incremental

solution are becoming apparent.

A second assumption that is highly problematic relates to geographic distribution of legal

immigrants. Although we can impute political geography from postal zip codes, we are less

certain that “intended residence” effectively measures actual residence. Moreover, subsequent

internal migration is currently estimated from data on matched tax returns. This means we

tacitly assume that the locality in which an immigrant intends to reside matches the locality

where he or she will first appear as the filer or as an exemption on a tax return.8 This assumption

is good if the immigration is employment-based, or if the immigrant is an immediate relative of

an employed person. If, on the other hand, the immigration event is associated with a temporary

sojourn in one locality during which a search for employment ensues that will ultimately result in

a move, the assumption fails. Moreover, one is inclined to suspect that the failure would

spuriously favor immigrant enclaves over areas that may feature greater job opportunities but

fewer immigrants. This represents a second useful area for research through alternative data

sources.

Migration of refugees

Refugees (RE) consist of people outside their country of nationality who are unable or unwilling

to return to that country because of persecution or a well-founded fear of persecution. After

residing in the United States for a minimum of one year (depending on the provisions of their

admission as refugees), they are allowed to adjust to legal immigrant status. Other classes of

 

8

 To estimate internal migration, IRS tax returns are collected and linked across years by the filer’s social security

number. Estimates in a specific geographic unit are created using data on each filer and the number of dependents

claimed.
U.S. Census Bureau

13

adjustees in the INS file are included via a “proxy rule” whereby we assume them equal in

number to people currently entering who will adjust in the future. There are two reasons that

refugees are treated differently. First, refugee movements are prompted by international

humanitarian crises and political upheavals, so refugee entries often occur in “waves” of arrivals.

A historical example of this was the Mariel boatlift, which brought 120,000 people into the

United States from Cuba over a matter of days in early 1980. Furthermore, because refugees

arrive through administrative decisions and receive financial aid from the government, there is a

viable administrative data source that provides numbers of refugees at time of arrival, rather than

at time of adjustment to immigrant status.

The number of refugees allowed to resettle in the United States each fiscal year is determined by

the President after consultation with Congress in relation to existing international humanitarian

developments. The President can also lift this ceiling throughout the year. Therefore, the

estimated number of refugees from 1990 to 2000, presented in Table 2, fluctuated annually

between a low of 78,000 in 1997-98 and a high of 128,000 in 1994-95. This sub-component

represents the third largest contributor to net international migration to the United States behind

legal immigration and unauthorized immigration.

Data sources

Estimates of the refugee population are based primarily on data provided by the Office of

Refugee Resettlement (ORR) of the Department of Health and Human Services (DHHS). This

data set reports the number of refugees by month of entry and the country of citizenship who are

eligible to receive benefits from DHHS. Although data are supplied on a monthly basis and tend

to be current, it is necessary to project a few additional months in a given cycle of population

estimation. Data sets used to impute characteristics for this population include the INS

microdata file and the 1990 decennial census.

Methodology

Although ORR tabulates the necessary data monthly, we must define them in such a way as to

facilitate a parallel exclusion of its members from the INS immigrant data for the fiscal year in

which they adjust status. Fortunately, refugee status is clearly identified in the laws governing

adjustment to immigrant status, and is therefore identifiable in the INS immigrant microdata via

class of admission. For example, migrants from the Mariel boatlift of 1980 were non-refugee

“parolees” who arrived in the United States and sought asylum. While asylees could be

identified as such in the INS data, it is not easy to identify the subset of these asylees for whom

separate administrative sources provide the number of total arrivals. Consequently, the treatment

of such situations in population accounting must be determined individually from their historical

context. In the case of Cubans, there was a blanket provision (until the late 1990s) allowing

virtually any Cuban arriving in the United States to adjust to immigrant status, usually after a

very brief interval of time. Fortunately, data on Cuban parolees have been available to the ORR,

so they could be included upon arrival and excluded from INS data for adjustments. A similar

but more limited provision existed for Haitians in the early 1980s. A small flow of Haitians

continued to arrive sporadically during the 1990s, and we received data on this group from ORR

as well. In the INS data, our strategy was to assume that this group was congruent with Haitian-
U.S. Census Bureau

14

born people adjusting to permanent resident status as asylees, so we excluded the latter group

from the immigrant data accordingly.

There remains the task of assigning demographic and geographic detail to the series. Three

fundamental assumptions are made in order to do this. The first is that the age and sex

composition of a given country of origin can be measured from INS data on refugees adjusting to

immigrant status, after adjusting age to account for the time elapsed from nonimmigrant arrival

to adjustment to legal permanent resident status. The second is that geography of intended

residence for refugees of a given country of origin at time of adjustment to immigrant status is

indicative of their geography of residence when they first appear on a tax return. The reason for

the emphasis on first tax return is that subsequent internal migration depends on an initial

location of tax filing. While this assumption is vulnerable to error, we deem it more robust than

an assumption that first appearance on a tax return would match the actual first residence of a

refugee on arrival in the country. The third assumption–familiar from our treatment of legal

immigrants–is that race and Hispanic origin composition can be deduced from the race and

Hispanic origin composition of recent foreign-born migrants to the United States of the same

country of birth in the 1990 census. All of these assumptions are made within country groups,

and for this purpose we assume that country of citizenship in the refugee data matches country of

birth in the INS immigrant data and 1990 census data on foreign-born migrants.

Having made these three assumptions, the assignment of characteristics is carried out by

simulating a microdata file, and using the assumptions to impose characteristics on simulated

records. Records are simulated to replicate the precise number of refugees and entrants from the

ORR series by month and country of citizenship. For each country group, the distribution by

state and county observed in the INS immigrant file for refugee adjustees is pro-rated to sum to

the refugee total for each fiscal year, and the resulting distribution is randomized (“without

replacement,” to yield a perfect match of the aggregate distribution) on the simulated refugee

microdata. A similar procedure is carried out for age and sex, using the refugee adjustees in the

INS file as a data base once again, and for race and Hispanic origin, but using the 1990 census

data on foreign-born migrants from 1985 to 1990 as a data base.

Strengths and limitations

Data for refugees are of high quality, because they rely directly on administrative sources. A

possible limitation, albeit small, to the quality of our estimates of total refugees at the national

level arises from assuming that people adjusting to immigrant status under a refugee provision,

or as asylees for the limited number we have assumed, are in fact the same people as those who

arrived and were included in the ORR data.

More problematic is the assignment of geographic detail based on the geographic patterns of

refugees adjusting to legal permanent resident status, and the assumed relationship of the latter to

location at time of first tax filing. Because the number of countries that are major suppliers of

refugees is rather small, understanding refugee groups through ethnographic case studies is

relatively promising.
U.S. Census Bureau

15

Net unauthorized migration to the United States

Often referred to as the “illegal” or “undocumented” population, the unauthorized migrant

population consists primarily of two groups: those entering the United States (primarily across

land borders) without inspection, and those entering the United States with legal temporary visas

who violate the terms or stay beyond the specified time allotment of their visa. This population,

by definition, is elusive and administrative data are impossible to collect. Therefore, indirect

estimation methods must be used to measure unauthorized migration patterns. Because it

represents a major contribution to net international migration, after legal migration, unauthorized

migration estimates may be the largest source of bias in the estimates of international migration.

Similar to other sub-components of net international migration, demographic changes in the

unauthorized population are influenced by changes in immigration law. A change in

immigration law that produced a substantial effect on the unauthorized population was the

Immigration Reform and Control Act (IRCA) of 1986. As noted in the legal immigration

section, this law granted legal status to a sizeable group of unauthorized residents in 1987 and

1988. More specifically, IRCA enabled about 1.6 million illegal immigrants to obtain legal

permanent residence in the United States by demonstrating that they had been continuously

resident in the United States since before January 1, 1982. A separate set of provisions also

extended legal permanent residence to about 1.1 million Special Agricultural Workers (SAWs)

who worked in perishable agricultural commodities at least 90 days in the United States in each

of three years before May 1, 1986, or for at least 90 days during the year ending May 1, 1986

(Smith et. al. 1996, INS 2000).

Beginning in 1985, the Census Bureau incorporated estimates of net unauthorized migration in

the national population estimates. Using a residual technique that examines the total foreignborn and the legal foreign-born population, Warren and Passel (1987) estimated that

approximately 2.1 million undocumented migrants were enumerated in the 1980 census. These

estimates combined with additional research using the Current Population Survey (CPS) from

1980 to 1983 provided the foundation to establish an estimate of a net annual increase of 200,000

unauthorized migrants for each year from 1980 to 1990 (U.S. Census Bureau 1986).

During the 1990s, the Census Bureau revised its estimates for unauthorized migration. Prior to

the release of 1990 census data, the results of two studies were combined to provide a

preliminary “point estimate” of 3.3 million unauthorized migrants living in the United States as

of April 1, 1990 (Woodrow 1991).9 Using several alternative estimates produced in the early

1990s, researchers reached a consensus estimate of 225,000 net annual additions to the

unauthorized population resulting from net migration for the 1990 decade (Robinson 1994).

From 1994 to the present, the constant assumption of 225,000 net unauthorized migrants was

applied to the national estimate for years ending June 30.

 

9

 For a detailed discussion of the preliminary April 1, 1990, stock estimate, refer to Woodrow, K.A. 1991.

“Demographic Analysis Evaluation Project D2: Preliminary Estimates of Undocumented Residents in 1990.” 1990

Decennial Census, Preliminary Research & Evaluation Memorandum no. 75.
U.S. Census Bureau

16

Data sources

In order to estimate net unauthorized migration for the 1990-2000 decade, multiple studies using

several data sets contribute to the final point or consensus estimates. Data sets used include: 1)

INS estimates of the unauthorized population; 2) the legal immigration file applied to the

national estimates described in the respective section; 3) 1990 decennial census data; 4) the

Current Population Survey (CPS); and 5) data collected for those granted legal status under

IRCA.

Methodology

In the early 1990s, several sets of independent estimates of the unauthorized population were

produced. Ranges of these alternative estimates were averaged to create the assumed number of

unauthorized foreign-born residents for inclusion in the production of national estimates. The

Urban Institute (Clark et. al. 1994) and the Census Bureau (Robinson 1994) produced these

independent estimates of the unauthorized population for 1990. The Census Bureau created two

separate sets of estimates, one adjusting for the undercount of the foreign-born population in the

1990 census, and the other not adjusting for undercount. Each set of estimates was measured by

using a residual technique that subtracts the legal resident foreign-born (LFB) population from

the total foreign-born (FB) population for each annual entry cohort of immigrants by country of

birth, who entered the United States between 1985 and 1990. Equation 3 presents the residual

equation used. To measure the number of legal permanent residents, the Census Bureau used the

legal immigration file (described in the Legal immigration section) combined with refugee

estimates (described in the Migration of refugees section). Similarly, the Urban Institute

tabulated the number of legal permanent residents by processing the INS microdata file

internally.

Equation 3. NU t-1, t = FB t-1, t – LFB t-1, t (3)

where

NU t-1, t = unauthorized immigrant population, arrived in the interval from time t-1 to time t;

FB t-1, t = foreign-born population arrived from time t-1 to time t; and

LFB t-1, t = legal resident foreign-born population arrived from time t-1 to time t.

Two estimates of net annual unauthorized migration were produced for each study. One estimate

measured the net annual migration based on those entering between 1985 and 1990; the second

estimate accounted for entrants from 1987 to 1990. Table 6 presents the range of net

unauthorized estimates produced. Averages of the preliminary estimates were created using

potential scenarios. The resulting averages range between a low of 211,000 net annual entrants

and a high of 245,000 net annual entrants (data not displayed). After averaging the resulting

averages, we selected 225,000 as an appropriate number to represent the net annual addition of

unauthorized migrants for the 1990-2000 decade. The estimate of 225,000 represents net annual

additions to the unauthorized population caused by migration only.

An independent estimate, produced by the INS (Warren 1992), further supported the final

assumption of an annual addition of 225,000 net unauthorized migrants. Using internal INS

data, the Current Population Survey, and the 1980 census, the INS estimate identified those who

overstay or violate their visa terms, those who enter without inspection, and those legalized

under IRCA. In addition, the estimate theoretically captures those potentially undercounted in
U.S. Census Bureau

17

the decennial census. The INS estimated that from 1988 to 1992, the United States experienced

a net annual increase of approximately 299,000 unauthorized migrants. Based on research by

Woodrow (1991) of the Census Bureau, the estimates of undercount of the total unauthorized

population in the 1990 census is assumed to range from 20 to 30 percent. If an assumption of a

25 percent undercount for the unauthorized population were applied to the INS net estimate, the

INS net estimate is reduced to approximately 224,000, an estimate near the final Census Bureau

assumption of 225,000.

After estimating net annual unauthorized migration, demographic characteristics were imputed.

For purposes of the vintage 2000 national estimates, the race and Hispanic origin distributions

for unauthorized net migration were derived from INS estimates of the unauthorized population

by country of birth for 1996 (Warren 1997). These estimates encompass both those entering

without inspection and nonimmigrants that overstay or violate the terms of their visa. After

categorizing the country of birth as mentioned in the Legal immigration section, these estimates

indicate that approximately 53 percent were born in Mexico, 26 percent were born in Other

North, Central, and South America (excluding Mexico, Cuba, and Canada), and 21 percent were

born in the remaining countries of the world. The age and sex distributions were imputed from

the data of unauthorized immigrants legalized in 1987 and 1988 under the IRCA law. The age

distribution was backdated from the year of legalization to the year of arrival.

Strengths and limitations

The strength of the Census Bureau’s methodology is in its partial use of decennial census data.

These data are more reliable than CPS data as the census data are collected from approximately

one in every six U.S. households, in comparison to the monthly sample of approximately 50,000

households participating in the national survey. Another important attribute of census data is

that it lends itself to census-level estimates of unauthorized migration because it excludes people

that would not be enumerated by a census, hence out of the population estimates universe. Its

limitations are primarily in its inability to track fluctuations in annual migration. Addressing this

weakness might entail examining alternative data sources and alternative methods for the

estimation of this hard-to-count population.

Currently, the estimates of the unauthorized population produced by the INS (Warren 1999) are

the most comprehensive and up to date. In comparison to the INS estimates published in 1996,

new estimates are created using a revised methodology based primarily on detailed demographic

analysis of annual INS administrative data and monthly CPS-based estimates of the foreign born

published by the Census Bureau. The INS has applied this methodology to create annual

estimates of the unauthorized population for the 1987 to 1997 period. In summary, the resulting

product provides estimates of the annual unauthorized population by sex and region of birth. The

main advantage to applying the current INS estimating technique is the availability of

information for annual trends, in contrast with the Census Bureau assumption of constant trends

throughout the 1980s and 1990s. Unfortunately, the estimates of country of birth do not provide

adequate detail for Census Bureau international migration estimates purposes because they are

aggregated for the following regions: Mexico, the rest of the Western Hemisphere, and the

Eastern Hemisphere.
U.S. Census Bureau

18

Emigration

Emigration (E) refers to the permanent departure from a country of residence. As a subcomponent of net international migration, emigration is defined as the number of U.S. permanent

residents departing from the United States to reside abroad. This population accounts for the

departure of both native and foreign-born legal residents. The departure of unauthorized

migrants, migrants from Puerto Rico, and temporary migrants, are excluded from this subcomponent in view of the fact that their respective components are already estimated net of

emigration.

Prior to 1957, the INS collected data on the annual number of emigrants leaving the U.S

allowing the Census Bureau to use this data for the national estimates. After 1957, the INS

discontinued collecting emigration data and the Census Bureau began using indirect methods to

measure this sub-component. Currently, estimates of the number of emigrants are produced

using two indirect techniques, differentiated by nativity status. Because neither method yields

current data, we projected constant trends for the decade.

According to estimates produced for the 2000 vintage, the number of emigrants increased each

year from 252,000 in 1990-91 to 279,000 in 1998-99. Throughout the decade (April 1, 1990 to

March 31, 2000), the total number of emigrants accumulated throughout the decade nearly 2.7

million.

Data sources

The sources of information used to estimate native and foreign-born emigration are entirely

different. The estimates of native emigration used foreign censuses and U.S. Department of

State data collected on citizens living abroad. Methodology used to estimate foreign-born

emigration is based on a residual technique comparing the foreign-born population in two

censuses.

Methodology: emigration of U.S. natives

Estimates of emigration for the native population are derived from research conducted by

Fernandez (1995). Data were collected from two separate types of sources, depending on the

availability for each country. The first of the sources, a pair of consecutive foreign censuses for

countries that enumerate their U.S.-born residents, was applicable for 11 countries (Australia,

Brazil, Canada, France, Great Britain, Ireland, Mexico, New Zealand, Sweden, Switzerland, and

Venezuela). Most of these sources provided age and sex of U.S. emigrants. The censuses

yielded an estimate of 20,977 emigrants for 1980.

The number of native U.S. emigrants estimated for the remaining countries without adequate

census data were derived using U.S. Department of State data. The Department of State collects

data on the number of U.S. residents that register at a U.S. post. Data for the total number of

residents were collected for 1970 and 1980. The age and sex distributions for each country were

imputed from the results of the foreign censuses reporting U.S. born people with a “similar

cultural background,” and are reported to “center” around 1980 (Fernandez 1995). The emigrant
U.S. Census Bureau

19

population was survived forward using the cohort survival method, resulting in an annual

average estimate of 27,204 U.S. emigrants for 1980.

The summation of the estimates from both sources resulted in an annual estimate of 48,000

native emigrants for 1980. For a detailed discussion of the methodology, consult the Population

Estimates and Projections Technical Working Paper No. 10. Again, this estimate is assumed to

remain constant each year.

Methodology: emigration of foreign-born legal residents

Estimates of foreign-born emigration are based on rates rather than the number of emigrants, as

is used for the native population. The annual rates are currently defined as the number of

foreign-born emigrants exiting the United States per year divided by the total number of legally

resident foreign born in the United States by age, sex, and country of birth (14 country

groupings). In 1994, Ahmed and Robinson published estimates of the number of foreign-born

emigrants who left between 1980 and 1990 in Population Estimates and Projections Technical

Working Paper No. 9.

Ahmed and Robinson used a residual technique pioneered by Warren and Peck (1975) that

involved comparing the foreign-born population in the 1990 census with the foreign-born

population enumerated in the 1980 census. In summary the expected foreign-born population is

calculated and compared to the foreign-born population enumerated in the 1990 census for two

different periods of entry, the foreign born that entered before 1980 and those entering between

1980 and 1990. Theoretically, the only events that should distinguish the two populations (the

expected vs. the enumerated) are mortality and emigration during the two periods. Mortality is

estimated by the application of life table survival rates to the foreign-born population by age and

sex to determine the size and characteristics of the population that would survive to a designated

period in the absence of emigration. Subtraction of the expected population from the foreignborn population self-identified as arriving before 1980 yields an estimate of emigration during

the decade.

Unfortunately, the coverage of the foreign-born population by the two censuses was inconsistent,

which produced bias in the results of any residual method that relied on intercensal comparisons.

Ahmed and Robinson addressed this issue by comparing about 40 country-of-birth categories,

and different decades of arrival, which allowed the identification of cross-categories of country

and period of arrival for which results were implausible. The most implausible results were

observed for countries that had a substantial component of unauthorized residents, whose

undercounts in the two censuses were large and inconsistent. Allowances were made for these

inconsistencies by imputing rates of emigration for countries with implausible results from

countries with similar but more plausible results. Ultimately, a schedule of rates of emigration

for four large country groups, age, and sex were determined that could be applied to the groups

during the intercensal decade, to produce an estimate of roughly 1.95 million emigrants from

1980 to 1990.

The estimate of emigration changed in the course of the 1990-2000 decade. Prior to 1994, we

assumed that there were 133,000 foreign-born emigrants per year (Ahmed and Robinson 1994).
U.S. Census Bureau

20

Beginning in 1994 and extending through 1996, we used an estimate of 195,000 per year, which

was adopted from research by Ahmed and Robinson. Although not explicit, the research by

Warren and Peck and Ahmed and Robinson suggest that the amount of emigration is related to

the previous flow of immigrants. To accommodate this finding, in 1997 we adopted a technique

whereby we estimate foreign-born emigration by crude rates applied to provisional legal foreignborn population totals for 40 countries. In 1998, we used some of the intermediate results of the

analysis by Ahmed and Robinson to generate annual age-specific rates of emigration–applicable

to the 1980s decade–for 14 country-of-birth groups (Oosse 1998). Because these rates were

generated from rate schedules for four groupings of countries, any inter-country variation among

the 14 was understated to non-existent. Nonetheless, these rates had the advantage of allowing

for a differentiation in the propensity to emigrate by age.

The resulting rates were assumed constant through the following decade of the 1990s, and when

applied to estimates of the legal foreign-born population as they were produced, by calendar

quarter, yielded current estimates of foreign-born emigrants. Age, sex, race, Hispanic origin, and

county of pre-emigration residence were imputed as a pro-rata of the foreign-born population

enumerated in the 1990 census.

Strengths and limitations

Emigration, similar to unauthorized migration, is a sub-component of net international migration

that is fraught with uncertainty. The estimates do not include current information, relying

instead on a constant projection (whether of numbers or rates) from a prior decade. The lag in

the availability of census data renders it impossible to update research on emigration of the sort

carried out by Ahmed and Robinson until about three years into the following decade.

In addition, the population universe enumerated in each census includes unauthorized

immigrants. Therefore, in order to estimate the emigration of the legal foreign-born population,

Ahmed and Robinson made assumptions about emigration trends from particular countries of

birth that are traditional sources of unauthorized migration to the United States. These

assumptions however may not have adequately accounted for the emigration of the unauthorized

population. Consequently, the estimates of annual emigration of the legal foreign-born

population may be overstated.

Net migration from Puerto Rico

Estimating migration flows between the United States and outlying areas under U.S. jurisdiction

presents a special problem because these flows represent migration of U.S. citizens. These

outlying areas principally include Puerto Rico, American Samoa, Guam, U.S. Virgin Islands, and

the Commonwealth of the Northern Mariana Islands. While we assume population movement to

and from most of these areas to net to zero, the estimated size of migration between Puerto Rico

and the United States is large enough to justify its incorporation as a sub-component of net

international migration. Little information is available about the current migration patterns from

Puerto Rico. Because Puerto Rico is an U.S. territory and most residents are citizens of the

United States, movement between the two places is not restricted; more importantly, it is not a

registered event. Therefore, we cannot rely on administrative data to estimate this migration
U.S. Census Bureau

21

pattern. We estimated a net annual addition of 12,646 migrants from Puerto Rico to the United

States each year, and assumed this was constant throughout the decade. The demographic

characteristics were also held constant throughout the decade.

Data and methodology

While a number of different approaches have been considered or attempted for estimating

migration to the United States from Puerto Rico, our current method depends on a projection of

constant net migration, based on a previous decade. The use of this projection entails three

distinct assumptions. First, we compute migration using the residual technique for the

intercensal period between the 1980 and 1990 censuses of Puerto Rico. Estimates of the net

migration from Puerto Rico by age and sex during the 1980s were derived by the International

Programs Center (IPC) of the U.S. Census Bureau. A 1980-based zero-migration estimate of the

population of Puerto Rico by age and sex for April 1, 1990, was created using the cohort

component method with vital registration data for births by sex and deaths by age and sex to

estimate a decade of population change, assuming the absence of migration to or from the island.

Subtracting this population (by age and sex) from the population enumerated in the 1990 census

yielded an estimate of the net effect of migration during the decade. This estimate excludes

deaths and includes births occurring to migrants after their arrival in Puerto Rico. Projecting the

surviving net migrants back to an estimated year of arrival using the cohort component method

and fertility and mortality rates by age and sex yielded an estimate of net migration excluding

births and including those who died. The resulting number is divided by 10 to produce an annual

estimate of net migration to Puerto Rico from the rest of the world during the decade. Potential

constraints for this estimate include differential underenumeration between the two Puerto Rican

censuses, as well as problems in the registration of births and deaths, including errors in the

identification of the place of residence between Puerto Rico and elsewhere.

This estimate of intercensal net migration to Puerto Rico includes not only the exchange of

migrants between the island and the 50 states and the District of Columbia, but also the exchange

between the island and the rest of the world. This leads to our second major assumption, which

is that the net of unauthorized migration to the island, net migration from other outlying areas to

the island, net movement of civilian and military personnel between the island and the rest of the

world (outside the United States) and all emigration (including legal residents) from the island to

the rest of the world is zero. While this assumption is plausible in an approximate sense, we

have no estimate for these components that would allow us to test the assumption. This leaves

one measurable component, namely legal migration from the rest of the world to Puerto Rico.

We assume that this is measured by the number of legal immigrants during the 1980s, as

recorded in INS public-use immigrant data files, that gave a Puerto Rican zip code for their

intended residence. As expected, the numerically dominant country of birth was the Dominican

Republic. Given all these assumptions, we were able to subtract this migration from the net

migration to the island for the decade, to yield an estimate of net migration from the United

States to the island, which we annualized by dividing by 10.

The final assumption, and probably the most vulnerable one, is that the net balance of migration

between Puerto Rico and the United States during the 1980s also applied to the 1990s.
U.S. Census Bureau

22

Having determined net migration by age and sex, we imputed a distribution by race and Hispanic

origin. The Puerto Rican censuses of 1980 and 1990 did not include questions on race or

Hispanic origin, so we relied on a tabulation of people enumerated in the U.S. census of 1990

who had resided in Puerto Rico in 1985 to establish the distribution by race and Hispanic origin.

Strengths and limitations

Although net migration from Puerto Rico ranks with the sub-components of emigration of legal

residents and net unauthorized migration as being difficult to estimate, the potential for

numerical error is smaller with this sub-component than with the other two.

While there are no administrative data that provide direct estimates of migration from Puerto

Rico, there are alternative approaches available that involves the use of current data.

Unfortunately, past results using these methods have rendered them either impractical or

incapable of producing plausible results.

One alternative method tried in the past relies on passenger traffic data in and out of the San Juan

airport. The registration of arrivals and departures is required of the various airlines that serve

this airport, and records are tabulated by the Puerto Rico Planning Board. When implemented in

the past, it produced results that were deemed implausible in the early 1990s because of two

significant problems with this data series. The first is that most passenger traffic represents

business travel and tourism, rather than actual changes in residence. Nevertheless, if registration

were complete and unbiased, it is assumed that any resulting balance in passenger traffic should

measure permanent moves in and out of Puerto Rico. On the other hand, even a relatively small

bias in the registration of arrivals with respect to that of departures could have a major effect on

the estimation of net migration, given that migration is such a small portion of overall passenger

traffic. The second problem is that the registration of each arrival and departure is not

implemented by all airlines. While this may not necessarily bias arrivals with respect to

departures, it renders the estimation of migration incomplete.

A second approach considered previously, but not applied, involves estimation of net migration

using IRS tax forms. This method is attractive because it is already the current method of

estimating migration among the 50 states and District of Columbia. Unfortunately, only a small

proportion of Puerto Rican residents are likely to appear on tax forms. Because average income

levels in Puerto Rico are substantially lower than those in any of the 50 states and the District of

Columbia, a large portion of wage earners have income levels below the threshold required to

file tax forms. Therefore, it cannot be assumed that the migratory behavior of tax filers and their

dependents would be representative of the migratory behavior of the population as a whole.

Net temporary migration

Recently, the sub-component of net temporary migration (NT) to the United States gained

importance in regard to population change. Net temporary migration refers to immigrants that

are issued temporary visas to stay in the United States for a predetermined amount of time.

Unlike legal immigrants, these people are not granted permanent residence and are therefore

referred to as nonimmigrants. Nonimmigrants consist largely of tourists and temporary business
U.S. Census Bureau

23

visitors. Because our estimated population universe refers to the resident population, tourists

and temporary business visitors are excluded from the estimate, as they are not likely to be

enumerated in the decennial census. The majority of immigrants classified as nonimmigrants for

the purposes of the national estimates generally fall under the following summarized categories:

1) foreign government officials, 2) students, 3) representatives to international organizations, 4)

temporary workers, 5) transit immigrants, 6) exchange visitors, 7) North American Free-Trade

Agreement (NAFTA) workers, 8) intra-company transferees, and 9) the spouses and children of

many of the summarized categories (INS 2000).

During the 1990-2000 decade, the Census Bureau began accounting for nonimmigrants in the net

international migration component for the national population estimates. Although certain

nonimmigrants are considered residents and may be enumerated in the decennial census, the

Census Bureau does not collect data on their legal permanent residence status at the time of

enumeration. Those adjusting to legal permanent resident status are measured in the legal

immigration sub-component using INS data described in the Legal immigration section.

Administrative data for nonimmigrants collected by the INS are unsuitable to the estimate

process until the nonimmigrant applies for legal permanent resident status. Therefore, indirect

methods are used to identify and estimate this population. Throughout the majority of the

decade, the Census Bureau relied on an assumption of constant net temporary migration, derived

from an estimate of the nonimmigrant population counted in the 1990 census. In the end of the

decade, the increasing number of specialty workers granted H-1B visas resulted in the need to

incorporate this growth in the nonimmigrant estimate. The numbers of nonimmigrants with

specialty workers assumed in the vintage 2000 estimates shown separately, is presented in Table

8.

Methodology: net temporary migration (Column A, Table 8)

In the early 1990s, the Census Bureau developed criteria to identify resident nonimmigrants

enumerated in the 1990 census (Word 2000). These criteria are based on visa eligibility

requirements and are defined by characteristics measured in the census that appear to match

these requirements. Based on these specifications, the Census Bureau identified a stock estimate

of 487,922 nonimmigrants enumerated in the 1990 census. This estimate provided the

demographic characteristics of nonimmigrants by age, sex, race, Hispanic origin, country of

birth, and place of residence. Appendix A contains a detailed discussion of the criteria

developed to identify nonimmigrants in the 1990 census.

After measuring the nonimmigrant population stock, we must estimate the net annual addition of

temporary migrants. Nonimmigrants are treated somewhat uniquely when estimating the U.S.

population, given that they do not remain in the population indefinitely as nonimmigrants.

During the course of a year, the nonimmigrant population loses people to emigration, death, or

adjustment to legal permanent resident status. New nonimmigrants are also added to the resident

population through migration, including some individuals who return to the United States more

than once.

In producing the estimates of net annual additions, the 1990 population of nonimmigrants was

projected one year using life tables. Under the assumption of constant net annual additions, the
U.S. Census Bureau

24

population by age does not change during the year. Hence, subtracting the constant population

by age from the one-year projection yielded the number of replacement nonimmigrants in each

age group needed to maintain the initial population, including its age composition.

The difference between the projection and the constant population in the all-ages total equaled

the number of deaths experienced in the nonimmigrant population. This was carried out for each

cross-category of race and Hispanic origin. In this way, we assume that the balance of entries,

departures, and adjustments to immigrant status are sufficient to ensure that each age-sex-raceHispanic origin category remains the same, while taking into account the aging of

nonimmigrants. Based on these assumptions and methodology, a net of 669 nonimmigrants was

estimated to enter the population each year, equal to the number who died during the year.

Geographic details to the county level for the net estimate of 669 temporary migrants were

obtained from the 1990 census.

Methodology: net specialty workers (Column B, Table 8)

The changing composition of the nonimmigrant population in recent years demanded a

reevaluation of the methodology used to identify nonimmigrants in the production of national

estimates. A growing population of temporary skilled or specialty workers with H-1B visas, who

are not specifically identified in the Census Bureau nonimmigrant estimates prior to the 2000

vintage, requires attention. In response to a demand for specialty workers, in the fall of 2000

Congress passed legislation that increased the cap on H-1B visas to 195,000 for each of the next

three years (FY 2000 through 2002). The H-1B visa limit had already been raised in 1998 from

65,000 to 115,000 workers for fiscal years 1999 and 2000, in order to relieve the backlog of

nonimmigrant applicants.

To measure the increase in the number of H-1B visas, a separate allowance was made for the

vintage 2000 national estimates. Unlike the constant assumption used in estimates through 1999,

the specialty worker population was allowed to change over time. This change is estimated by

using the number of nonimmigrant H-1B visas issued each year (Lowell 2000), and deducting an

allowance for deaths, emigration, and adjustment to immigrant status. Because of an increase in

the number of H-1B admissions beginning in the late 1980s, the net H-1B population increased

throughout the early 1990s. In response to this growth in the specialty worker population, an

annual limit of 65,000 H-1B visas was imposed by Congress beginning in 1992. Until this limit

was raised in 1998, the number of special temporary workers entering the United States was

assumed sufficient to make up for the loss of the pre-1992 temporary workers to death,

emigration, and adjustment. The outcome was a net allowance of zero H-1B workers between

1993 and 1997. The legislation that raised the limit on H-1B visas in 1998 resulted in a further

substantial increase in the specialty worker component at the end of the decade. Table 8 shows

the allowance for H-1B specialty workers estimated for the vintage 2000 estimates.

After producing the estimate of the annual net flow of H-1B specialty workers for 1990-2000,

demographic characteristics were imputed. Country of birth was assigned using Lowell’s (2000)

estimates of H-1 entries by country of birth (from Department of State visa issuance data). Age,
U.S. Census Bureau

25

sex, county and state of residence were allocated using INS data on nonimmigrants that adjusted

their status to legal permanent resident and identified their last nonimmigrant visa category as

H-1. The age of specialty workers was backdated to the age at the year of initial arrival to the

United States, as was done for other sub-components. Race and Hispanic origin were imputed

using 1990 census data on the foreign-born population with years of entry 1985-1990, by country

of birth.

Strengths and limitations

The Census Bureau is currently considering a separate estimate for foreign students to be

incorporated in population estimates. Like H-1B workers, the number of students from abroad

has increased in recent years, suggesting that the assumed increase in the nonimmigrant

population stock – even after allowing for specialty workers – is too low.

The criteria used to identify potential nonimmigrants enumerated in the census also must be

reevaluated for future estimates. Although the basic criteria for nonimmigrants have remained

the same, the characteristics of specific classes of nonimmigrants should be re-evaluated to be

certain they accurately reflect eligibility requirements. The constant assumption estimate did not

include certain classes of nonimmigrants (e.g. foreign government officials and North American

Free-Trade Agreement workers) that should be included in future estimates. Additionally, in

order to prevent possible underestimates of the nonimmigrant population, the Census Bureau

should compare its estimates against estimates produced by other researchers, such as those

produced by the INS and the Urban Institute (Clark and Passel 2000).

Another limitation to the current estimates of the nonimmigrant population is that by making a

separate allowance for H-1B workers from the net annual addition of nonimmigrants, the H-1B

population may be overcounted. In all likelihood, the original net annual estimate included some

nonimmigrants with H-1B visas; therefore, a separate estimate of the H-1B population based on

administrative records may include individuals already captured in the net annual estimate.

However, this potential overcount is likely offset by the fact that dependents of H-1B workers

were not included in the H-1B estimate, and that not all classes of nonimmigrants were included

in the 1990 constant estimate.

III. CONCLUSION

The sub-components aggregated to estimate net international migration to the United States are

difficult to estimate and are not simply the compilation of both gross immigration and emigration

from the United States. Some estimates rely predominately on indirect methods to measure both

the stock and flow of these populations. Compared to each component of change, the subcomponents of net international migration, in particular emigration, net unauthorized migration,

and net temporary migration, in all likelihood present the largest sources of bias to the estimates

series. As a major determinant to population change, it is necessary that the Census Bureau

continuously evaluates and updates the methodologies, data sources, assumptions, and

definitions used to create these estimates. This document provides an avenue for discussion and
U.S. Census Bureau

26

evaluation of how well the Census Bureau estimates net international migration to the United

States as an input to the national estimates series.
U.S. Census Bureau

27

REFERENCES

Ahmed, B. and J.G. Robinson. 1994. “Estimates of Emigration of the Foreign-born Population: 1980-

1990.” Population Estimates and Projections Technical Working Paper No. 9, U.S. Census

Bureau.

Clark, R.L. and J.S. Passel. 2000. “Groping in the Dark: One Solution to the Immigrant Policy/Data

Gap.” The Urban Institute. Washington, D.C.

Clark, R.L., J.S. Passel, W.N. Zimmermann, and M.E. Fix. 1994. "Fiscal Impacts of Undocumented

Aliens: Selected Estimates for Seven States.” Urban Institute Unpublished Paper.

Fernandez, E.W. 1995. “Estimation of the Annual Emigration of U.S. Born Persons.” Population

Estimates and Projections Technical Working Paper No. 10, U.S. Census Bureau.

Immigration and Naturalization Service, U.S. Department of Justice. 2000. Statistical Yearbook of the

Immigration and Naturalization Service, 1998. U.S. Government Printing Office: Washington,

D.C.

Lowell, B.L. 2000. “H-1B Temporary Workers: Estimating the population.” Institute for the Study of

International Migration, Georgetown University.

Oosse, M. 1998. “Calculation of Annual Emigration Rates for the Foreign-Born, 1980-1990.”

Unpublished Memorandum.

Robinson, J.G. 1994. “Clarification and Documentation of Estimates of Emigration and Undocumented

Immigration.” Unpublished Memorandum.

Sater, D.K. 1994. “Geographic Coding of Administrative Records—Current Research in

Zip/Sector-to-County Coding Process.” Population Estimates and Projections Technical Working

Paper No. 7, U.S. Census Bureau.

Smith, S., R.G. Kramer, and A. Singer. 1996. Effects of the Immigration Reform and Control Act:

Characteristics and Labor Market Behavior of the Legalized Population Five Years Following

Legalization. Bureau of International Labor Affairs, U.S. Department of Labor.

United Nations. 2000. “Protocol relating to the Status of Refugees of 31 January 1967.”

http://www.unhcr.ch/refworld/refworld/legal/instrume/asylum/proteng.htm

United States Census Bureau, Population Division. 1986. Estimates of the Population of the United

States, by Age, Sex, and Race: 1980 to 1985. U.S. Government Printing Office, Washington,

D.C.

Warren, R. 1999. “Unauthorized Immigrants Residing in the United States: Estimating the Population,

Components of Change, and Trends, by Broad Area of Origin, 1987 to 1997.” Presented at the

annual meetings of the Population Association of America, March 25-27, New York.

_____. 1997. “Estimates of the Undocumented Immigrant Population Residing in the United States:

October 1996.” Office of Policy and Planning, U.S. Immigration and Naturalization Service.

_____. 1992. “Estimates of the Resident Illegal Alien Population: October 1992.” Unpublished

Memorandum.

Warren, R. and J.S. Passel. 1987. “A Count of the Uncountable: Estimates of Undocumented Aliens

Counted in the 1980 United States Census.” Demography 24(3): 375-393.

Warren, R. and J. Peck. 1975. “Emigration from the United States: 1960 to 1970.” Presented at the

annual meeting of the Population Association of America, April 17-19, Seattle.

Woodrow, K.A. 1991. “Demographic Analysis Evaluation Project D2: Preliminary Estimates of

Undocumented Residents in 1990.” 1990 Decennial Census, Preliminary Research & Evaluation

Memorandum No. 75.

Word, D.L. 2000. Personal Communication.

_____. 1992. “The Census Bureau Approach for Allocating International Migration to States, Counties,

and Places: 1981-1991.” Population Estimates and Projections Technical Working Paper No. 1,

U.S. Census Bureau.
U.S. Census Bureau

28

Table 1. The total resident population and net international migration component for the vintage 2000 post-censal national estimates: 1990 to 2000.

[Resident population. July 1 to June 30]

Initial Net Crude 

Year resident international NIM rate

population 1 Number Percent migration (NIM) Number Percent (per 1,000)

1990 (4/1-6/30) 248,790,925 679,614 0.3 177,456 NA NA NA

1990-1991 249,470,539 2,737,998 1.1 698,732 93,603 13.4 2.8

1991-1992 252,208,537 2,895,490 1.1 792,335 34,231 4.3 3.1

1992-1993 255,104,027 2,753,595 1.1 826,566 -63,302 -7.7 3.2

1993-1994 257,857,622 2,543,469 1.0 763,264 20,620 2.7 3.0

1994-1995 260,401,091 2,475,423 1.0 783,884 78,910 10.1 3.0

1995-1996 262,876,514 2,423,821 0.9 862,794 68,027 7.9 3.3

1996-1997 265,300,335 2,546,406 1.0 930,821 -46,549 -5.0 3.5

1997-1998 267,846,741 2,487,690 0.9 884,272 -21,427 -2.4 3.3

1998-1999 270,334,431 2,453,054 0.9 862,845 (NA) (NA) 3.2

1999-2000 (7/1-4/1) 272,787,485 1,820,861 0.7 649,032 (NA) (NA) (NA)

Total (as of 4/1/00) 274,608,346 25,817,421 9.4 8,232,001 (NA) (NA) (NA)

1 The April 1, 1990 population is generally not adjusted for underenumeration, but includes specific modifications for certain areas from the

Census Test of 1995 and the Dress Rehearsal of 1998. This number also includes census count resolution corrections. The population of

248,709,873 appearing in 1990 census publications excludes these additions.

(NA) Not available.

Change in

population

Change in

NIM
U.S. Census Bureau

29

Table 2. Net international migration and its sub-components for the vintage 2000 post-censal national estimates: 1990 to 2000.

[July 1 to June 30]

Net Movement Net migration Net Net

international Legal of from unauthorized temporary

migration immigration refugees Puerto Rico migration migration Emigration

1990 (4/1-6/30) 177,456 147,404 27,362 3,153 56,096 6,323 62,882

1990-1991 698,732 576,801 85,578 12,646 225,000 50,416 251,709

1991-1992 792,335 666,123 121,772 12,646 225,000 20,592 253,798

1992-1993 826,566 725,515 118,144 12,646 225,000 2,433 257,172

1993-1994 763,264 670,067 115,233 12,646 225,000 669 260,351

1994-1995 783,884 680,300 127,670 12,646 225,000 669 262,401

1995-1996 862,794 782,132 108,642 12,646 225,000 669 266,295

1996-1997 930,821 883,471 79,568 12,646 225,000 669 270,533

1997-1998 884,272 843,674 78,331 12,646 225,000 669 276,048

1998-1999 862,845 731,170 101,170 12,646 225,000 72,063 279,204

1999-2000 (7/1-4/1) 649,032 536,329 72,238 9,502 169,057 74,110 212,204

Total (as of 4/1/00) 8,232,001 7,242,986 1,035,708 126,469 2,250,153 229,282 2,652,597

Year
U.S. Census Bureau

30

Table 3. Distribution of legal immigration by major class of admission from the

Immigration and Naturalization Service: fiscal year 1998.

Subject to Percent of INS

numeric limit legal immigration

 Immediate relatives of U.S. citizens no 43

 Other family-sponsored immigrants yes 29

 Employment immigrants yes 12

 Refugees and asylees no 1

8

 Diversity immigrants yes 7

 Other no 2

1

Total (x) 100

1 Annual numeric limits of refugees are determined by the President after consultation

 with Congress and can be lifted by the President throughout the year.

2 "Other" contains special categories which are generally unlimited (e.g. Cuban and Haitian entrants).

Source: Immigration and Naturalization Service. 2000. "Table A Class of Admission

of Legal Immigrants: Fiscal Years 1988-98." Statistical Yearbook of the Immigration 

and Naturalization Service, 1998. U.S. Government Printing Office: Washington: DC.

(x) Not Applicable.

Class of admission
U.S. Census Bureau

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Table 4. Net international migration and legal immigration numeric change, percent change, and crude net legal

immigration rate for the vintage 2000 post-censal national estimates: 1990 to 2000.

[July 1 to June 30]

Net Percent Crude net legal

international Legal of immigration rate

migration (NIM) immigration NIM Number Percent (per 1,000)

1990 (4/1-6/30) 177,456 147,404 83.1 NA NA NA

1990-1991 698,732 576,801 82.5 89,322 15.5 2.3

1991-1992 792,335 666,123 84.1 59,392 8.9 2.6

1992-1993 826,566 725,515 87.8 -55,448 -7.6 2.8

1993-1994 763,264 670,067 87.8 10,233 1.5 2.6

1994-1995 783,884 680,300 86.8 101,832 15.0 2.6

1995-1996 862,794 782,132 90.7 101,339 13.0 3.0

1996-1997 930,821 883,471 94.9 -39,797 -4.5 3.3

1997-1998 884,272 843,674 95.4 -112,504 -13.3 3.1

1998-1999 862,845 731,170 84.7 (NA) (NA) 2.7

1999-2000 (7/1-4/1) 649,032 536,329 82.6 (NA) (NA) (NA)

Total (as of 4/1/00) 8,232,001 7,242,986 88.0 (NA) (NA) (NA)

(NA) Not available.

Change in legal immigration

Year
U.S. Census Bureau

32

Table 5. Legal immigrants by country of birth categories for the federal fiscal year ending September 30, as applied to the vintage 2000 post-censal national estimates:

1990 to 1999.

1990 1

1991 1992 1993 1994 1995 1996 1997 1998 1999

Mexico 23,589 51,071 90,429 108,345 106,649 117,986 137,159 206,781 189,291 179,533

Cuba 1,141 2,126 1,735 1,985 2,630 5,948 3,962 3,814 2,787 6,300

Canada 6,884 12,080 14,920 16,950 15,987 17,985 17,903 19,338 16,780 11,942

Latin North & Central America 28,344 73,796 80,447 92,211 79,414 74,715 75,574 83,836 68,463 75,067

Other North and Central America 21,362 42,374 31,464 38,945 37,996 45,187 49,032 58,004 46,760 47,276

South America 23,450 46,345 49,823 52,127 46,563 58,181 65,165 74,874 61,204 53,079

Europe 31,109 61,608 91,712 92,590 93,713 85,452 79,879 85,943 75,055 63,188

Former USSR 1,055 5,706 10,372 13,154 13,111 20,561 23,101 26,343 21,973 23,485

Middle East 16,413 33,776 37,470 37,361 29,863 34,923 35,923 37,220 31,969 27,648

China and Taiwan 25,186 50,476 60,009 57,616 43,870 48,863 59,666 59,205 53,340 45,832

India 14,533 31,126 34,560 39,993 34,876 40,176 47,615 48,131 44,358 35,821

Japan and Korea 17,384 26,003 29,662 24,427 21,873 25,644 24,588 27,043 26,101 21,181

Philippines 30,444 53,043 57,276 60,326 51,367 54,341 54,262 55,076 40,832 34,924

Other South and East Asia 35,206 70,808 81,358 63,278 43,896 53,263 54,809 64,740 58,577 56,050

Africa 9,275 19,677 21,198 22,858 21,381 45,548 49,333 54,961 46,072 40,633

Oceania 2,119 4,027 4,482 4,705 4,530 5,902 5,623 5,939 5,130 4,496

Abroad, at sea, and other 0 0 1 0 2 2 101 657 1,310 1,055

Total 287,494 584,042 696,918 726,871 647,721 734,677 783,695 911,905 790,002 727,510

1 Data interval from April 1, 1990 to September 30, 1990.

Country of birth

Federal fiscal year ending September 30
U.S. Census Bureau

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Table 6. Alternative estimates of annual net additions of the unauthorized migrant population, 

analyzed in selecting the estimate of 225,000 per year. 

Type and source of estimate Net annual estimate Rationale for estimate

"Counted" Unauthorized

Urban Institute (Clark et.al. 1994) 195,000 Residual estimates based on analysis of 

224,000 1990 census and INS data. The first 

estimate (195,000) is implied from estimate

of unauthorized residents who entered 

1985-90, the second (224,000) is indicated

by estimate of unauthorized residents

who entered 1987-90.

Census Bureau (1) 226,000 Residual estimates based on analysis of 

244,000 1990 census and INS data. The first 

estimate (226,000) is indicated by estimate

of unauthorized residents who entered 1985-

90, the second estimate (244,000) is implied

from estimate of unauthorized residents.

Census Bureau (2) 249,000 Based on the same data as Census Bureau

266,000 (1) above, but with one modification: an

allowance is made for census undercount

of the foreign-born population (using

Post Enumeration Survey factors) in 

calculation of the residual estimates of the 

unauthorized resident population.

Total Unauthorized

 INS (Warren 1992) 299,000 Estimates based on detailed analysis of 

visa overstayers and data on persons who

legalized under IRCA. 

Source: Robinson, J.G. 1994. "Clarification and Documentation of Estimates of Emigration 

 and Undocumented Immigration." Unpublished U.S. Census Bureau Memorandum. 
U.S. Census Bureau

34

Table 7. Emigrants by nativity for the vintage 2000 post-censal national estimates: 1990 to 2000.

[July 1 to June 30]

Number Percent Estimate Percent Estimate Percent

1990 (4/1-6/30) 62,882 NA NA 11,967 19.0 50,915 81.0

1990-1991 251,709 2,089 0.8 48,000 19.1 203,709 80.9

1991-1992 253,798 3,374 1.3 48,000 18.9 205,798 81.1

1992-1993 257,172 3,179 1.2 48,000 18.7 209,172 81.3

1993-1994 260,351 2,050 0.8 48,000 18.4 212,351 81.6

1994-1995 262,401 3,894 1.5 48,000 18.3 214,401 81.7

1995-1996 266,295 4,238 1.6 48,000 18.0 218,295 82.0

1996-1997 270,533 5,515 2.0 48,000 17.7 222,533 82.3

1997-1998 276,048 3,156 1.1 48,000 17.4 228,048 82.6

1998-1999 279,204 (NA) (NA) 48,000 17.2 231,204 82.8

1999-2000 (7/1/-4/1) 212,204 (NA) (NA) 36,066 17.0 176,138 83.0

Total (as of 4/1/00) 2,652,597 (NA) (NA) 480,033 18.1 2,172,564 81.9

(NA) Not available.

Native emigrants Foreign-born emigrants

Year

Emigrants

Change in Emigrants
U.S. Census Bureau

35

Table 8. Nonimmigrants by special worker H-1B visa status for the vintage 2000 post-censal

national estimates: 1990 to 2000.

[July 1 to June 30]

Net Net Total net

temporary specialty worker temporary

migration visas (H-1B) migration

(A) (B) (A) + (B)

1990 (4/1-6/30) 167 6,156 6,323

1990-1991 669 49,747 50,416

1991-1992 669 19,923 20,592

1992-1993 669 1,764 2,433

1993-1994 669 0 669

1994-1995 669 0 669

1995-1996 669 0 669

1996-1997 669 0 669

1997-1998 669 0 669

1998-1999 669 71,394 72,063

1999-2000 (7/1/-4/1) 502 73,441 74,110

Total (as of 4/1/00) 6,690 222,425 229,282

Year
U.S. Census Bureau

36

Appendix A. Identification of nonimmigrants for the 1990 census

The estimation of temporary legal migration required the identification of a population of

nonimmigrants in the 1990 census. Because legal permanent residence status is not asked by the

census, various characteristics available from the census long form were used to impute

nonimmigrant status.

The Census Bureau first used three basic criteria to identify potential nonimmigrants: they could

not be a native or naturalized U.S. citizen on April 1, 1990; they had to have entered the United

States between 1987 and 1990; and they could not be living with a spouse or a related

householder who was a U.S. native or naturalized citizen.

If an individual met these basic criteria, they were then classified into one of the following

nonimmigrant visa categories: foreign college students, high school exchange students, scholars,

nurses, Jamaican agricultural workers, intracompany transferees, Canadian visitors

(“snowbirds”), au pairs, and the spouses and children of these nonimmigrants. These categories

were not exhaustive of all the nonimmigrant visa types, but they represented the majority of the

temporary residents in the United States in the early 1990s.

Foreign students attending U.S. colleges or graduate schools comprise a large portion of the

nonimmigrant population as estimated by the Census Bureau. According to the Census Bureau’s

criteria, a foreign student had to be enrolled in school and have at least a high school diploma.

Since law prohibits most foreign students from being employed while studying in the United

States, an individual was not classified as a foreign student unless they also were not working

full-time at the time of the census. In order to be identified as a foreign student, then, a person

must have also been either not currently in the labor force, had only worked 20 hours or less in

the preceding week, were not at work in the preceding week, or were unemployed and their

income during 1989 was less than $5,000.

The U.S. Department of State also issues separate nonimmigrant visas for the spouses and

children of foreign students. In order to be classified as one of these “student dependents,” a

person must have been living in a household with either a spouse or a parent (natural or

adoptive) who met the above criteria for a foreign student (enrolled in school, at least high

school diploma, etc.). The exceptions were spouses who also themselves met the criteria for

students. This condition prevented their misclassification as student dependents in cases where

both spouses were foreign students. Children who met the conditions for foreign students were

not excluded from the student dependent population in the Census Bureau estimates.

In addition to foreign college students, the Census Bureau also specified foreign high school

exchange students in its nonimmigrant population. Foreign high school students had to be

between the ages of 14 and 18, be enrolled in high school (grades 9 through 12), and could not

be a relative to their householder. There must also have been at least one other child in their

household who was between the ages of 14 and 18, and their householder had to be a U.S. citizen

(either native or naturalized). These last criteria presumably came from knowledge of exchange

student programs that place foreign high school students in the homes of families who already

have a child attending the student’s destination school.
U.S. Census Bureau

37

A scholar had to have at least a Master’s degree; they also had to have a health diagnosing

(including physicians, dentists, and veterinarians) or post-secondary teaching occupation, or had

to have worked in the hospital or college and university industry.

A nurse must have had at least some college, as well as an occupation in health assessment and

treatment (such as nurses, pharmacists, or therapists) or health services (dental assistants,

orderlies, etc.), and had to work in the hospital or nursing and personal care facilities industries.

A nonimmigrant born in Jamaica whose occupation was coded as “agricultural and related” was

assumed to be a Jamaican agricultural worker.

Nonimmigrants identified as having a visa for intracompany transferees must have been at least

30 years old and had at least a Bachelor’s degree on April 1, 1990. They must also have been

currently employed, and reported an income of either $0 or minimum of $35,000.

Spouses and children of scholars, nurses, Jamaican agricultural workers, and intracompany

transferees who did not also meet the criteria for these classifications were assumed to be

dependents of these types of nonimmigrants, similar to the classification of student dependents.

These dependents are also included in the nonimmigrant population.

Canadian nonimmigrants with a B-2 tourist visa, often referred to as “snowbirds,” are Canadian

citizens who spend part of the year in the United States. A snowbird could have any relationship

to their householder (including being the householder themselves), but they must have either

been born in Canada or had a spouse who was born in Canada. The underlying assumption about

this category of nonimmigrants was that they were probably retired individuals who spent a

significant part of the year vacationing in the United States; therefore they (or their spouse) also

must have been at least 55 years old and could not be in the labor force. In addition to these

criteria, Canadian B-2 nonimmigrants must have had no U.S. natives in their household,

although household members who were naturalized citizens were allowed.

An additional nonimmigrant visa category identified by the Census Bureau was that of foreign

private childcare workers, or au pairs. A nonimmigrant who was believed to be an au pair must

have been female and between the ages of 18 and 29. She must have been born in Europe, had at

least a high school diploma, not be a relative to the householder, and have had a private

household service occupation. Finally, the au pair’s householder must have been a native of the

United States or a naturalized citizen and there had to be at least one child under age 12 in the

household, who was assumed to be the subject of the au pair’s care taking.

The criteria for identifying nonimmigrants enumerated in the 1990 census has not been modified

by the Census Bureau since the original estimate was made in the early 1990s.
U.S. Census Bureau

38

POPULATION DIVISION WORKING PAPER SERIES

For copies of these working papers, please contact the Statistical Information Staff, Population Division, U.S.

Census Bureau, Washington, DC 20233-8800 (301) 457-2422/pop@census.gov

NO. 1 - "The Census Bureau Approach for Allocating International Migration to States, Counties, and Places:

1981-1991." David L. Word. October 1992.

NO. 2 - "Geographic Coding of Administrative Records--Past Experience and Current Research." Douglas

K.Sater. April 1993.

NO. 3 - "Postcensal Population Estimates: States, Counties, and Places." John F. Long. August 1993.

NO. 4 - "Evaluating the Passel-Word Spanish Surname List: 1990 Decennial Census Post Enumeration Survey

Results." R. Colby Perkins. August 1993.

NO. 5 - "Evaluation of Postcensal County Estimates for the 1980s." Sam T. Davis. March 1994.

NO. 6 - "Metropolitan Growth and Expansion in the 1980s." Richard L. Forstall and James D. Fitzsimmons. April

1993.

NO. 7 - "Geographic Coding of Administrative Records – Current Research in ZIP/Sector-to-County Coding

Process." Douglas K. Sater. June 1994.

NO. 8 - "Illustrative Ranges of the Distribution of Undocumented Immigrants by State." Edward W. Fernandez

and J. Gregory Robinson. October 1994.

NO. 9 - "Estimates of Emigration of the Foreign-Born Population: 1980-l990." Bashir Ahmed and J. Gregory

Robinson. December 1994.

NO. 10 - "Estimation of the Annual Emigration of U.S. Born Persons by Using Foreign Censuses and Selected

Administrative Data: Circa 1980.” Edward W. Fernandez. January 1995.

NO. ll - "Using Analytic Techniques to Evaluate the 1990 Census Coverage of Young Hispanics." Edward

Fernandez. May 1995.

NO. 12 -"Metropolitan and Nonmetropolitan Areas: New Approaches to Geographical Definition." Donald C.

Dahmann and James D. Fitzsimmons. October 1995.

NO. 13 - "Building a Spanish Surname List for the 1990's--A New Approach to An Old Problem." David L. Word

and R. Colby Perkins, Jr. February 1996.

NO. 14 - "Fertility of American Men." Amara Bachu. March 1996.

NO. 15 - "Comparisons of Selected Social and Economic Characteristics Between Asians, Hawaiians, Pacific

Islanders, and American Indians (Including Alaskan Natives)." Edward W. Fernandez. June 1996.

NO. 16 - "Findings on Questions on Race and Hispanic Origin Tested in the 1996 National Content Survey."

Prepared in the Population Division by the Racial Statistics Branch and the Ethnic and Hispanic Statistics

Branch. December 1996.

NO. 17 - "Race and Ethnicity Classification Consistency Between the Census Bureau and the National Center for

Health Statistics." Larry Sink. February 1997.

NO. 18 - "Results of the 1996 Race and Ethnic Targeted Test." May 1997.

NO. 19 - "Who Responds/Who Doesn’t? Analyzing Variation in Mail Response Rates During the 1990 Census."

David L. Word. July 1997.

NO. 20 - "Trends in Marital Status of U.S. Women at First Birth: 1930 to 1994." Amara Bachu. March 1998.

NO. 21 - "State Estimates of Organized Child Care Facilities." Lynne Casper and Martin O’Connell. March 1998.

NO. 22 - "How Well Does the Current Population Survey Measure the Foreign-Born Population in the United

States" Dianne Schmidley and J. Gregory Robinson. April 1998.

NO. 23 - "Poverty, Family Structure, and Child Well-Being: Indicators from the SIPP." Jason Fields and Kristin

Smith. April 1998.

NO. 24 - "Child Well-Being Indicators from the SIPP." Kristin Smith, Loretta Bass, and Jason Fields. April 1998

NO. 25 - "Timing of First Births: 1930-34, 1990-94." Amara Bachu. May 1998.

NO. 26 - "Co-Resident Grandparents and Grandchildren: Grandparent Maintained Families." Lynne Casper and

Ken Bryson. May 1998.

NO. 27 - "Population of the 100 Largest Cities and Other Urban Places in the United States: 1790 to 1990."

Campbell Gibson. June 1998.

NO. 28 - "Are There Differences in Voting Behavior Between Naturalized and Native-born Americans?" Loretta E.

Bass and Lynne M. Casper. March 1999.
U.S. Census Bureau

39

NO. 29 - "Historical Census Statistics on the Foreign-born Population of the United States: 1850-1990." Campbell

J. Gibson. February 1999.

NO. 30 - "Direct Measures of Poverty as Indicators of Economic Need: Evidence from the Survey of Income and

Program Participation." Kurt J. Bauman. November 1998.

NO. 31 - "American Community Survey and Intercensal Population Estimates: Where Are the Cross-roads?" Amy

Symens. December 1998.

NO. 32 - "Women’s Labor Force Attachment Patterns and Maternity Leave: A Review of the Literature." Kristen

Smith and Amara Bachu. January 1999.

NO. 33 - "Evaluation of Relationship, Marital Status, and Grandparents Items on the Census 2000 Dress

Rehearsal." Charles Clark and Jason Fields. April 1999.

NO. 34 - "Unbinding the Ties: Edit Effects of Marital Status on Same Gender Couples." Charles Clark and Jason

Fields. April 1999.

NO. 35 - "Racial-Ethnic and Gender Differences in Returns to Cohabitation and Marriage: Evidence from the

Current Population Survey." Philip N. Cohen. May 1999.

NO. 36 - "How Does POSSLQ Measure Up? Historical Estimates of Cohabitation." Lynne Casper, Philip N.

Cohen, and Tavia Simmons. May 1999.

NO. 37 - "Childlessness Among American Women On the Rise?". Amara Bachu. May 1999.

NO. 38 - "Methodology and Assumptions for the Population Projections of the United States: 1999 to 2100.”

Frederick Hollman, Tammany Mulder, and Jeffrey Kallan. October 1999.

NO. 39 - "What Do We Know About the Undercount of Children?" Kirsten K. West and J. Gregory Robinson.

August 1999.

NO. 40 - "Birth Expectations of Women: New Data from June 1998 Current Population Survey.” Amara Bachu

and Kristen Smith. Release Pending.

NO. 41 - "Trends in Labor Force and Employment Characteristics of Married-Couple Families With or Without

Children." Amara Bachu. Release Pending.

NO. 42 - "Measures of Help Available to Households in Need: Their Relationship to Well-Being, Welfare, and

Work." Kurt Bauman and Barbara Downs. May 2000.

NO. 43 - "Have We Reached the Top? Educational Attainment Projections of the U.S. Population.” Jennifer

Cheeseman Day and Kurt Bauman. May 2000.

NO. 44 - "The Emerging American Voter: An Examination of the Increase in the Black Vote in November 1998.”

Avalaura L. Gaither and Eric C. Newburger. June 2000.

NO. 45 - "An Analysis of State and County Population Changes by Characteristics: 1990-1999." Amy Symens

Smith, Bashir Ahmed, and Larry Sink. November 2000.

NO. 46 - "The Effect of Work and Welfare on Living Conditions in Single Parent Households.” Kurt Bauman.

August 2000.

NO. 47 - "Projections of the Number of Households and Families in the United States: 1999 to 2025.” Monique

Oosse and Ching li Wang. Release Pending.

NO. 48 - "Fertility in the United States: Is State-Level Fertility Converging to the National Level?" Laura Heaton.

Release Pending.

NO. 49 – “Variation in State Mortality over Time.” Monica Oosse. Release Pending.

NO. 50 - “Accuracy of the U.S. Census Bureau National Population Projections and Their Respective Components

of Change.” Tammany Mulder. Release Pending.

NO. 51 - “U.S. Census Bureau Measurement of Net International Migration to the United States: 1990 to 2000.”

Tammany Mulder, Frederick Hollmann, Lisa Lollock, Rachel Cassidy, Joseph Costanzo, and Josephine

Baker.