Mexican migration to the United States is the largest sustained international movement anywhere in the world. During the 1960s, legal Mexican immigration totaled 430,000 persons; but in the 1970s, it grew to more than 680,000, and by the 1980s, it reached the remarkable figure of 3 million (U.S. Immigration and Naturalization Service [INSI, 1992). Woodrow and Passel (1990) estimate that another 800,000 Mexicans arrived without documents between 1980 and 1990, and official statistics reveal that some 12 million entered the United States as temporary visitors (INS, 1992). During the first half of the 1990s, 2.2 million legal Mexican immigrants arrived, exceeding the record pace set during the prior decade (INS, 1996). Since 1942, when labor recruitment from Mexico last began, at least 6.3 million Mexicans have immigrated to the United States.
In a recent article, Massey and Espinosa (1997) argued that three fundamental forces account for the high and rising rate of immigration from Mexico. The first is market consolidation, which involves the extension of capitalist markets into less-competitive sectors of the Mexican economy, a force given considerable impetus by the enactment of the North American Free Trade Agreement on January 1, 1994. Although of great importance in understanding Mexican immigration, this force is not of primary interest here. The other two forces--social capital formation and human capital accumulation--ate directly related to the analysis we seek to undertake.
Social capital emanates from interpersonal ties that acquire instrumental value for Mexicans seeking to enter the United States and find a job. People who have already been to the U.S. are in a position to help friends and relatives travel northward, cross the border, and obtain work by providing information, contacts, and material assistance (Espinosa, 1997; Espinosa and Massey, 1997). Ties to current or former migrants thus yield social capital: people socially connected to U.S. migrants are more likely to emigrate themselves, and each act of migration creates additional social capital that encourages still more migration. According to Massey and Espinosa (1997:989), "After more than 50 years of continuous development, this process of social capital formation is well-advanced and largely self-sustaining ... so that social capital ... is very widely diffused throughout the Mexican population."
Human capital refers to knowledge, skills, and experience that enhance an individual's potential value as an economic actor. Among migrants to the United States, the most important kind of human capital comes from migratory experience itself, which is accumulated across successive U.S. trips. The more experience a migrant has crossing the border, living in the United States, and working in U.S. labor markets, the lower the potential costs and the higher the likely benefits of migrating again. As a result, the probability of making additional trips rises with each trip taken. The more one migrates, the more one is likely to continue migrating, yielding a self-reinforcing cycle of human capital formation. Once again Massey and Espinosa (1997:989) state that "after 50 years of constant movement back and forth, the human capital necessary to support mass migration is also widely diffused throughout Mexico."
The importance of human and social capital to migration decisions has been well documented. Studies repeatedly have shown that Mexicans with prior U.S. experience, or with ties to persons with such experience, exhibit a markedly greater probability of emigrating than those who lack these resources (see Massey et al., 1987; Massey and Garcia Espana, 1987; Kossoudji, 1992; Taylor, 1986, 1987; Jasso and Rosenzweig, 1988; Zahniser, 1996). Despite Massey and Espinosa's (1997:987) bald assertion that human and social capital are "widely diffused throughout Mexico," however, no study has actually documented this fact. To date there has been no attempt either to count the relative number of Mexicans with U.S. experience, or to determine the share who have some tie to a current or former U.S. migrant. If these numbers are both small, then the potential for future emigration will be limited no matter what the effect of U.S. experience or social ties on the odds of out-migration; but if either of the numbers is large, t he potential for future migration is considerable.
In this paper we draw upon a unique data set to describe the stock of migration-relevant human and social capital available to residents of western Mexico. After presenting the average level and distribution of U.S. experience among Mexican residents, we document the kind, number, and range of social ties they have to current and former U.S. migrants. We then estimate a model to predict, from prior experience and social connections, the odds of U.S. migration and use the model to estimate the annual probability of emigration typical for men in western Mexico today. We conclude by considering the implications of our analysis for the future of Mexico-U.S. migration and discuss how results might be generalized to Mexico as a whole.
Our data come from the Mexican Migration Project (MMP), which in 1982 and successive years from 1987 to 1994, surveyed two to five Mexican communities annually using simple random-sampling methods. The surveys were generally conducted in December and January, when seasonal migrants return to Mexico and are available for interviewing. The sample size was typically two hundred households, unless the community had fewer than five hundred residents, in which case a smaller number of households was selected.
The thirty-eight communities analyzed for this study are all located in western Mexico and were not chosen using probability mechanisms, but were purposely selected to incorporate a variety of population sizes, geographic situations, ethnic compositions, economic bases, and migratory experiences (see Massey, Goldring, and Durand, 1994; Massey and Espinosa, 1997). Information about the communities and samples is summarized in Table 1. The communities vary in size from under 300 persons to almost 3 million, yielding an average size of around 92,000 inhabitants. Although our sample is not strictly representative of the states of western Mexico, it contains a broad cross section of households and communities in the region and …