Confronta i metodi

	Residual Method for Unauthorized Population	Dual-Systems Estimation of Irregular Migration
Campo	Migration Studies	Migration Studies
Famiglia	Process / pipeline	Process / pipeline
Anno di origine	1987	2003
Ideatore	Robert Warren and Jeffrey S. Passel	Peter van der Heijden, Maarten Cruyff, and colleagues; Dankmar Böhning
Tipo	Demographic-accounting estimation pipeline for unauthorized population	Administrative-record linkage and population-size-estimation pipeline
Fonte seminale	Warren, R., & Passel, J. S. (1987). A Count of the Uncountable: Estimates of Undocumented Aliens Counted in the 1980 United States Census. Demography, 24(3), 375-393.	van der Heijden, P. G. M., Cruyff, M., & van Houwelingen, H. C. (2003). Estimating the Size of a Criminal Population from Police Records Using the Truncated Poisson Regression Model. Statistica Neerlandica, 57(3), 289-304.
Alias	Demographic Residual Method, Warren-Passel Residual Method, Census-Minus-Legal Residual, Unauthorized Foreign-Born Residual	Dual-System Estimation, Multiple-Systems Estimation of Irregular Migration, Capture-Recapture for Irregular Migrants, Truncated-Poisson Population Estimation
Correlati	3	3
Sintesi	The residual method estimates the size of the unauthorized migrant population by subtraction: it takes the total foreign-born population counted in a census or large survey and removes the part that can be accounted for as legally resident, treating whatever remains as the unauthorized residual. Robert Warren and Jeffrey Passel introduced and validated the approach in their landmark 1987 Demography article, which matched undocumented aliens counted in the 1980 United States census against administrative records of legal immigrants. The arithmetic is deceptively simple, but the credibility of the estimate lives entirely in the adjustments. The legally resident stock must be aged forward from admission records and reduced for those who have since died or emigrated, and the resulting residual must be inflated to account for the share of unauthorized migrants the census itself failed to count. Done carefully and computed within detailed demographic cells — by age, sex, country of birth, and period of entry — the method turns two imperfect data sources that each say nothing directly about legal status into a defensible national estimate. It remains the dominant approach used by United States statistical agencies and research centers to size the unauthorized population.	Dual-systems estimation, the two-list special case of capture-recapture, estimates how many irregular migrants exist by exploiting the overlap between administrative records that each capture only part of the population. The logic is borrowed from wildlife ecology: tag animals on one trapping occasion, see how many tagged animals reappear on a second, and the rate of overlap reveals how many were never caught at all. Applied to migration, the 'traps' become administrative lists — police apprehension records, hospital registers, deportation files — and the people who appear on no list are the quantity to be estimated. Van der Heijden, Cruyff, and colleagues showed in their 2003 Statistica Neerlandica paper that even a single police register can support estimation through the truncated-Poisson model, by using how often individuals are recorded to infer how many were never recorded. Böhning, van der Heijden, and Bunge's 2018 monograph consolidated the modern toolkit for the social and medical sciences, with explicit treatment of the two assumptions that make or break the method: that lists are not too strongly dependent and that the population is not too heterogeneous in its chance of being captured. The output is a defensible estimate of an irregular-migrant total that, by definition, no register sees in full.