Sammenlign metoder

	Dual-Systems Estimation of Irregular Migration	Migrant Stock Estimation
Fagfelt	Migration Studies	Migration Studies
Familie	Process / pipeline	Process / pipeline
Opprinnelsesår	2003	1983
Opphavsperson	Peter van der Heijden, Maarten Cruyff, and colleagues; Dankmar Böhning	United Nations Population Division (standard measurement conventions)
Type	Administrative-record linkage and population-size-estimation pipeline	Cross-source pipeline for counting the resident migrant population
Opprinnelig kilde	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.	United Nations (1983). Manual on Methods of Estimating Internal Migration (Manual VI). Population Studies No. 47. New York: United Nations.
Alias	Dual-System Estimation, Multiple-Systems Estimation of Irregular Migration, Capture-Recapture for Irregular Migrants, Truncated-Poisson Population Estimation	Foreign-Born Stock Estimation, International Migrant Stock, Migrant Population Counting, Stock-Based Migration Measurement
Relaterte	3	3
Sammendrag	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.	Migrant stock estimation answers a deceptively basic question: how many migrants are living in a place at a given moment? Unlike migration flows, which count moves over an interval, a stock is a cross-sectional count of people whose origin differs from their place of residence — most commonly the foreign-born, but sometimes the foreign-national or those who have lived abroad. The United Nations measurement conventions, set out in its migration manuals, fix the core definitions (place of birth versus citizenship, duration thresholds, usual residence) and the at-risk concepts that make stocks comparable. In practice the analyst rarely has one clean source: censuses give place-of-birth tables but miss recent or irregular arrivals, population registers give continuous citizenship-based counts but vary in how they handle departures, and surveys give detail but suffer sampling error. Migrant stock estimation is therefore a pipeline that compiles these sources, harmonizes their differing definitions and geographies, and adjusts for undercount, overstay, and double counting, drawing on the same comparability concerns Bell and colleagues raised for internal migration. The output — a coherent count of migrants by origin, age, and sex — underpins integration policy, flow estimation, and the denominators of countless migration indicators.