economically into the U.S. labor market? This issue is dealt with in the section on economic assimilation below.

Are there intrinsic differences in relative productivity across immigrant cohorts? If so, why? Such cohort effects can arise from changes in immigration policy; one consequence of the major changes in policy embodied in the Immigration and Nationality Act Amendments of 1965, for example, may have been to deemphasize the role of skills in allocating entry visas. Later immigrants may thus have been less skilled relative to the native-born than those who came earlier.

Cohort effects may also stem from changes in economic or political conditions in the source countries and in the United States. Even if the United States had not adopted the 1965 amendments, the improvements in economic conditions in Western Europe would have reduced the number of immigrants from these historical source countries. If skill levels vary across countries or if skills from different countries are not equally transferable to the United States, then the changing mix in national origins of the immigrant flow generates cohort effects. 7

To determine whether such cohort effects indeed exist, it is instructive to summarize the key trends in some measures of skills over the past three decades.8 Table 5.5 reports both the distribution of educational attainment as well as the percentage wage differential between immigrant and native workers over this period; it presents data on men and women separately.

While comparing the skills and wages of immigrants with those of the native-born, it is important not to lose of sight of trends in the absolute skill levels of newly arriving immigrants. Table 5.5 shows, for example, that the education levels of new immigrant cohorts (men or women) have been rising over time. If education is a proxy for skill, the labor market skills that immigrants bring with them thus have been improving over time—but so have the skills of native-born Americans. The question, then, is whether the secular rate of improvement in immigrant skills has kept up with that of the native-born.

Education may be the central credential an immigrant carries when he or she arrives in the United States. Many immigrants come with impressive schooling. In fact, a larger proportion of recent new immigrants have at least a bachelor's

7  

Cohort effects are also observed when there is nonrandom return migration. If low-wage immigrant workers return to their source countries, the survivors from the earlier waves will tend to have relatively higher earnings than more recent waves. This issue is dealt with in the section on emigration below.

8  

The statistics presented in this chapter are typically obtained from calculations that use the Public Use Samples of the U.S. decennial census. For the most part, native and immigrant wages are calculated in the subsample of civilian workers who are between the ages of 25 and 64, and who are not self-employed. It is common to restrict the analysis of wage data to salaried workers because the income of self-employed workers reflects both a return to the workers' human capital as well as a return to the physical capital invested in the firm. The census does not provide any information on these separate components of a worker's income.



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