|Number of Mexican Households in Survey Sample with Migration Experience||Total Number of Mexican Households That Would Need to Be Sampled by the Survey|
migration. Specifically, sample sizes should be sufficiently large so as to accurately detect relatively small changes in flow rates (i.e., by a few percentage points) associated with changes in enforcement policies, market forces, and other factors. Some simple calculations by the panel using information from ENOE illustrate the challenges at hand, both for existing surveys as well as any new ones that may be put in place to specifically address the migration question. Table 4-1 shows the total number of households across Mexico that would need to be sampled in any given time period (be it quarterly or yearly) in order to obtain a target number of sampled households with “migration experience” (i.e., having crossed, or intending to cross, the U.S.–Mexico land border). The panel made two assumptions. The first assumption is that roughly 1.5 percent of households in Mexico each year have an individual who crosses the border. This assumption is based on a recent per person out-migration rate in ENOE of 3.78 per 1,000 (0.00378 percent) (Instituto Nacional de Estadística y Geografía, 2012), with average household size being around four people. The second assumption, based on documentation material for ENOE (Instituto Nacional de Estadística y Geografía, 2007:48), is that the survey response rate is approximately 85 percent. The number of households that would need to be interviewed is equal to the target sample size divided by the product of the response rate and the household out-migration rate.2 It is possible, in principle, to reduce sample sizes by oversampling in traditional Mexican “sending regions” or by otherwise using stratification or clustering based on what is known about the migration process to date. However, as discussed in Chapter 2, the sampling design would have to be adaptive to changing patterns of population migration, and strategies for oversampling could all too easily become out of date.
Total sample sizes would have to be even larger if one wanted precise flow estimates by, for example, each of the nine geographic sectors into
2 For example, 1,000/(0.015 * 0.85) = 78,431.