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.
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