on gathering social, demographic, and economic information on Mexican households and their U.S. migration experience. The MMP is supported by grants from the National Institute of Child Health and Human Development and the William and Flora Hewlett Foundation. MMP data are made available to the public through a website housed at Princeton University.

Each year during December and January (when seasonal and other migrants typically return home), the MMP randomly samples 200 households in several communities located throughout Mexico (for a total of 600 to 1,000 households interviewed per year). MMP communities are not randomly selected but are chosen to reflect a broad range of sizes, locations, urbanicity, and migration prevalence. Once communities have been chosen, frames are constructed by the enumeration of all households in smaller communities or all households in a neighborhood in larger metropolitan areas. Households are randomly selected within communities from among eligible households.

After gathering social, demographic, and economic information on the household and its members, interviewers collect basic information on each migrant’s first and last trip to the United States. From household heads who have migrated in the past, they compile a year-by-year retrospective history of U.S. migration and administer a detailed series of questions about the last trip northward, focusing on employment, earnings, and use of U.S. social services.

Following completion of the Mexican surveys, U.S.-based samples are gathered in some cases. Using tips from community contacts where available, interviewers travel to destination areas in the United States the following summer to administer identical questionnaires to migrants from the same communities sampled in Mexico; the exact number of migrants sampled (typically 10-20) depends on how many, if any, can be identified. These are permanent migrants who have settled north of the border and no longer return home. U.S.-based sampling is intended to generate a binational sample that is representative of permanent and return migrants. However, while most of the MMP communities sampled before 2000 have a U.S. counterpart, the majority sampled in 2000 and later do not. Because the U.S. sample is very small and limited to certain years, the MMP disproportionately represents return migrants and underrepresents permanent emigrants.

The data include community-based weights that reflect the community population. In the Mexican sample, the weight is calculated as the inverse of the sampling fraction where the number of households interviewed is divided by the number of eligible households in the predefined survey area from which the 200 surveyed households were drawn. The U.S. weight is also the inverse of the sampling fraction; the population size is estimated by comparing the number of adult children among surveyed household heads



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