ies, LaLonde and Topel's (1992) estimate for young black natives, implies that a 10 percent increase in the number of immigrants would decrease the wages of young black natives by only 0.6 percent.

Most of the studies focus on the relationship between native earnings and the immigrant share in the local labor market, but some also estimate the correlation between immigration and native labor force participation rates, hours worked, and unemployment rates. Panel B of Table 5.20, taken from Borjas's survey article, illustrates the findings of such studies. The available cross-city evidence also suggests that immigration has a weak effect on the employment of natives. Altonji and Card's (1991) study, for example, finds an elasticity that would imply that a 10 percent increase in the number of immigrants in a local labor market would reduce weeks worked by less skilled natives by 0.6 percent.

Studies of specific labor markets confirm these findings even when the market receives very large numbers of immigrants. On April 20, 1980, Fidel Castro declared that Cuban nationals wishing to move to the United States could leave freely from the port of Mariel. By September 1980, about 125,000 Cubans, mostly unskilled workers, had chosen to undertake the journey. Almost overnight, Miami's labor force had unexpectedly grown by 7 percent. Card's (1990) analysis of the data indicates that the time-series trend in wages and employment opportunities for Miami's workers, including its black population, was barely nudged by the Mariel flow. The trend between 1980 and 1985 was similar to that in other cities, such as Los Angeles, Houston, and Atlanta, which did not experience the Mariel flow.

The evidence also indicates that the numerically weak relationship between native wages and immigration is observed across all types of native workers, white and black, skilled and unskilled, male and female. The one group that appears to suffer significant negative effects from new immigrants are earlier waves of immigrants, according to many studies. For instance, Grossman (1982) reports that a 10 percent increase in the number of immigrants reduces the immigrant wage by 2 percent, and Altonji and Card (1991) conclude that a 10 percent increase in the number of immigrants reduces the immigrant wage by at least 4 percent.

Many of the studies make a particular effort to measure the impact of immigration on the wages and employment of specific subgroups of the native population, particularly black Americans. Because immigrants are relatively unskilled, some suspect that black workers may be particularly hard-hit by immigration. However, a look at Table 5.20 reveals that the estimated effects on both employment and wages are small even when estimated separately for blacks. None of the available evidence on spatial correlations suggests that in the aggregate the economic opportunities of black Americans are substantially reduced by immigration.

One reason for this perhaps surprising result is that black Americans and immigrants live in quite different areas of the country. For each black American

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