Confronta i metodi

	Multiplicity Sampling of Migrant Stock	Time-Location Sampling
Campo	Migration Studies	Migration Studies
Famiglia	Process / pipeline	Process / pipeline
Anno di origine	1970	2001
Ideatore	Monroe G. Sirken	CDC Community Intervention Trial for Youth study team (Muhib, Stueve, and colleagues)
Tipo	Network-based survey design and weighting estimator for rare populations	Probability-sampling pipeline for hard-to-reach mobile populations
Fonte seminale	Sirken, M. G. (1970). Household Surveys with Multiplicity. Journal of the American Statistical Association, 65(329), 257-266.	Muhib, F. B., Lin, L. S., Stueve, A., Miller, R. L., Ford, W. L., Johnson, W. D., & Smith, P. J. (2001). A Venue-Based Method for Sampling Hard-to-Reach Populations. Public Health Reports, 116(Suppl 1), 216-222.
Alias	Network Sampling of Migrants, Multiplicity Survey of Emigrants, Sirken Multiplicity Estimator, Relative-Report Migrant Sampling	Venue-Based Sampling, Time-Space Sampling, Venue-Day-Time Sampling, VDTS
Correlati	3	3
Sintesi	Multiplicity sampling, introduced by Monroe Sirken in 1970, is a survey design for counting rare and hard-to-reach populations by letting respondents report not only about themselves but about eligible relatives living elsewhere. For migration research the appeal is direct: emigrants and dispersed migrants are, by definition, absent from the sampling frame of the place that wants to count them, so an ordinary household survey misses them. Under multiplicity sampling a sampled household reports its migrant relatives — say, children or siblings who have moved abroad — according to an explicit counting rule, which dramatically raises the effective coverage of the rare group because many households can each contribute reports. The price of this expanded reach is that the same migrant may be reportable by several households, so each reported migrant must be weighted by the inverse of the number of households eligible to report them, the migrant's 'multiplicity.' Sirken showed that this multiplicity-weighted estimator is unbiased and that, by enlarging the set of reporters, it can sharply reduce the sampling variance for rare populations compared with conventional surveys.	Time-location sampling, also called venue-based or venue-day-time sampling, is a probability-sampling method for reaching populations that lack any list frame but reliably congregate at identifiable places and times. Developed and codified by Muhib, Stueve, and colleagues in a 2001 Public Health Reports article for a CDC youth study, it replaces the impossible task of enumerating a hidden population with the tractable task of enumerating the venues, days, and time slots where that population gathers. The analyst first builds an ethnographic frame of venue-day-time (VDT) units, then draws units at random, intercepts and enrolls eligible attendees on site, and finally weights respondents by how often they attend so that frequent venue-goers do not dominate the estimate. Because selection probabilities are known at each stage, the design yields defensible, variance-estimable population quantities rather than a convenience sample. For migration research it is especially valuable: day laborers at hiring corners, migrants at remittance shops, consulates, places of worship, markets, and transit hubs are mobile and unlisted, but they are observable in space and time. The method thus converts the visibility of a mobile migrant population into a genuine sampling frame.