Unauthorized Immigrants: Length of Residency, Patterns of Parenthood
Appendix B: Methodology
The data presented in this report on unauthorized and legal immigrants were developed with essentially the same methods used for previous reports (Passel and Cohn 2011, 2010). The estimates use a multistage estimation process, principally using March Supplements to the Current Population Survey (CPS). The CPS is a monthly survey of about 55,000 households conducted by the Census Bureau for the U.S. Bureau of Labor Statistics; the sample is expanded to about 80,000 households for the March supplement.
The first stage in the estimation process uses CPS data as a basis for estimating the number of legal and unauthorized immigrants included in the survey and the total number in the country using a residual estimation methodology. This method compares an estimate of the number of immigrants residing legally in the country with the total number in the CPS; the difference is assumed to be the number of unauthorized immigrants in the CPS. The legal resident immigrant population is estimated by applying demographic methods to counts of legal admissions covering the period from 1980 to the present, which are obtained from the Department of Homeland Security’s Office of Immigration Statistics and its predecessor at the Immigration and Naturalization Service. The initial estimates here are calculated separately for age-gender groups in six states (California, Texas, Florida, New York, Illinois and New Jersey) and the balance of the country; within these areas, the estimates are further subdivided into immigrant populations from 35 countries or groups of countries by period of arrival in the United States. Variants of the residual method have been widely used and are generally accepted as the best current estimates. For more details, see Passel and Cohn 2010 and Passel 2007.
Then, having estimated the number of legal and unauthorized immigrants in the March CPS Supplements, we assign individual foreign-born respondents in the survey a specific status (one option being unauthorized immigrant) based on the individual’s demographic, social, economic, geographic and family characteristics. The data and methods for the overall process were developed initially at the Urban Institute by Passel and Clark (especially 1998) and were extended by work of Passel, Van Hook and Bean (2004) and by subsequent work at the Pew Hispanic Center.
The final step adjusts the estimates of legal and unauthorized immigrants counted in the survey for omissions. The basic information on coverage is drawn principally from comparisons with Mexican data, U.S. mortality data and specialized surveys conducted at the time of the 2000 Census (Bean et al. 1998; Capps et al. 2002; Marcelli and Ong 2002). These adjustments increase the estimate of the legal foreign-born population, generally by 1-3%, and the unauthorized immigrant population by 10-15%. The individual survey weights are adjusted to account for immigrants missing from the survey. These augmented files serve as a basis for the detailed tabulations of the family, social, economic and geographic characteristics presented here and in previous reports.