Coming to the U.S. by Air:

A Lower Bound To Immigration Estimates

By Edwin S. Rubenstein

President, ESR Research

 

As the native population growth rate has fallen, net foreign immigration has come to constitute a larger and larger share of overall U.S. population growth. The size of this net inflow is not known with precision, however, and this constitutes the largest unknown in American population statistics. Despite the uncertainty, there has emerged a consensus among demographers and public policy analysts on its probable range.

After dropping to relatively low levels during the period 1931 to 1970, legal immigration to the United States has increased significantly in recent decades, primarily as a result of a change in immigration law in 1965. (see Table 1) According to the U.S. Immigration and Naturalization Service (INS), 7.6 million people attained legal permanent residence in the United States in the fiscal year 1991 to 1998 period. That comes to an average of  845,000 annually -- equaling the peak levels of immigration early in the Twentieth Century.

Table 1. Legal immigration to the United States: 1901 to 1998

Years

Legal Immigrants

 

Average per Year

1901-10

8,795,386

879,539

1911-20

5,735,811

573,581

1921-30

4,107,209

410,721

1931-40

528,431

52,843

1941-50

1,035,039

103.504

1951-60

2,515,479

251,548

1961-70

3,321,677

332,168

1971-80

4,493,314

449,331

1981-90

7,338,062

733,806

1991-98

7,605,068

845,008

                                              Source: 1998 INS Yearbook.

At the end of the 1990s about 950,000 legal immigrants per year wer coming into the U.S., according to the INS. If this figure is correct, immigration accounts for more than one quarter of the country's total population increase. Consequently, accurate estimates of the total U.S. population are highly dependent upon accurate statistics on legal immigration.

How accurate is the immigration figure? Twenty years ago population researcher Daniel R. Vining, Jr. tested the validity of consensus immigration figures by estimating a plausible “lower bound” to net U.S. immigration.(footnote 1)  Vining focused on one component of the net inflow of persons to the United States, namely, their net flow by commercial airlines, which, assuming that net migration by land, sea, and by clandestine and noncommercial air is positive, provides a lower limit for total U.S. immigration.

 

A lower bound is only interesting, of course, if it proves surprisingly high. The  official U.S. government tally of  arriving and departing air passengers certainly satisfies this criterion. In 2000, for example, the excess of  arriving over departing international air passengers was 4.718 million, according to the U.S. DOT. (Table 2.) For the entire decade (1990 to 2000)  it averaged 3.689 million  per annum. When Vining looked at this data in the late 1970s, he found the excess to be about 1 million.

 

 

Table 2:   International Air Passenger Arrivals to and From the United States

(Thousands)

 

 

Year

 

 

Arrivals (A)

 

Departures (D)

 

Total

(A + D)

 

 

Net (A - D)

 

Retention Rate

(A-D)/A

1960

2,566

2,336

4,902

230

9.0%

1970

9,874

9,096

18,970

778

7.9%

1975

12,646

12,053

24,699

593

4.7%

1980

20,262

19,256

39,518

1,006

5.0%

1985

24,156

22,487

46,643

1,669

6.9%

1990

36,414

34,046

70,460

2,368

6.5%

1991

35,464

33,286

68,750

2,178

6.1%

1992

38,927

36,211

75,138

2,716

7.0%

1993

41,558

38,254

79,812

3,304

8.0%

1994

43,818

40,349

84,167

3,469

7.9%

1995

46,910

43,026

89,936

3,884

8.3%

1996

49,853

45,785

95,638

4,068

8.2%

1997

54,315

49,684

103,999

4,631

8.5%

1998

56,181

50,863

107,044

5,318

9.5%

1999

57,785

53,856

111,641

3,929

6.8%

2000

62,217

57,499

119,716

4,718

7.6%

Ann. Avg.,

1990-2000

47,586

43,896

91,482

3,689

7.7%

SOURCE: U.S. DOT, National Transportation Statistics 2001, Tables 1-37 and 1-38; Air Carrier Profile (Appendix A). <http://www.bts.gov/publications/nts/index.html>

 

 

 

 

 

 

 

 

 

 

Interestingly, while the number of international passengers has risen by over 4-fold, the percentage difference between arriving and departing international passengers, which Vining calls the “retention rate,” has hardly changed at all: it was 7.8% in the 1970s, and was 7.7% in the 1990s. The constancy seems to imply that the impact of commercial air travel on U.S. immigration has risen in lock step with the number of airline passengers coming into the U.S.

 

The gap between international arrivals and departures (4.7 million in 2000) exceeds even the largest estimates made by demographers and government population experts of  total net immigration into the United States. Part of the problem appears to be attributable to a systematic undercount of departures on flights on flights leaving the United States – but only a part. Vining found a systematic undercount of passengers departing on charter flights in the government statistics. The problem still exists: In contrast with most other countries, the U.S. has no exit controls at airports. While the DOT and INS (and, presumably, its successor agency) assures that the proper forms are filled out on flights arriving in the U.S., both chartered and scheduled, because all incoming passengers must pass through immigration and customs and because the federal agencies want their own counts to tally with those of the air carriers, they are less careful about recording outbound passengers. Outbound charter flights in particular are cited as not complying with the paperwork, and thus creating a large undercount of outbound international passengers.

 

Moreover, DOT rules regarding its basic international air traffic report (the T-100 report) had, until recently, exempted air carriers that operate aircraft with 60 seats or less. Therefore passenger volume in particular markets – particularly the Caribbean and certain Canadian markets – is understated due to the large amount of service provided by small aircraft.

 

Statistical coverage of international airline traffic was the goal of  Federal legislation passed in the wake of 9/11. The Enhanced Border Security and Visa Entry Reform Act (HR 3525) that passed Congress last May requires U.S. citizens traveling abroad to reveal their identities and travel plans. For the first time government officials will monitor everyone who comes or goes from the United States as part of an overall strategy to enhance national security. Expanded monitoring is a first step toward a long-delayed automated entry/exit system for tracking visitors at U.S. ports of entry.

 

            Although electronic tracking of all arriving and departing air passengers was to start on January 1, 2003, INS did not publish the proposed new rule in the Federal Register until February. The air passenger data requirement will not formally take effect until the final rule is published, sometime after the 30-day comment period. In addition, since there is normally a six-month lag before airline passenger data are publicly released, comprehensive data on international arrivals and departures will not be available until later this year.

 

 

Vining's "solution" to flawed government statistics was to use air passenger statistics independently collected by individual airports as well as by the International Air Transport  Association (IATA) on air passenger travel to and from the U.S. over the North Atlantic – statistics that there is no reason to believe undercount departures relative to arrivals. The non-government data suggested a 50 to 60 percent smaller gap between arrivals and departures. Vining reported that government data on scheduled international flights, which in contrast to the charter flight data appear to be unbiased, were also consistent with this estimate.

 

Unfortunately, recent figures on arrivals and departures on scheduled international air flights are not readily available from DOT or the IATA. However, if we apply  the  retention rate for scheduled flights reported by Dr. Vining (3.8%) to current air passenger traffic volumes, we get an estimate of  2.4 million net arrivals in 2000 instead of the 4.7 million reported by the government. A more conservative approach would simply cut Vining’s retention rate in half, giving us an estimated million 1.2 million net  arrivals in 2000.

 

Even this lower figure for airborne immigration is substantially above recent INS estimates of  total net immigration to the U.S., which, of course, includes net migration by sea and land as well. The large disparity indicates either increasingly large scale underreporting of departing air passengers (even on scheduled flights) or a gross underestimate of U.S. immigration rates. Clearly further research is needed to resolve the question.

 

 

 

 

 

 

 

 

 

1. Daniel R. Vining, Jr., “Net Migration by Commercial Air: A Lower Bound on Total Net Migration to the United States,” Research in Population Economics, Volume 4, pages 333-350, 1982.