many aspects of the question a modern consensus of scholarly opinion cannot be found.
The economic impact of immigration is a complex issue and one that simple models of supply and demand do not address very well. Indeed, even predictions derived from elaborate general equilibrium models are only as good as the assumed linkages across disparate sectors of the economy. Because of the complexity of the social science, it has become easy for partisans in the debate to ignore scholarly work altogether or to pick and choose studies compatible with their preconceptions from the wide array of findings reported in the literature.
Nevertheless, we believe that it is possible to survey the literature and extract a list of tentative conclusions. These identify rather dramatic differences in the immigrant flows and in immigration's probable impacts between the earlier era of mass immigration and immigration today.
Not everyone will agree with our distillation nor welcome our attempt to cover such an intractable subject with the guise of apparent order. Our "findings" might be better read as provocation for further research. Nevertheless, the process of writing this chapter has convinced us, at least, that this entire area is ripe with important and researchable topics. To encourage debate, we begin by summarizing our findings regarding four interrelated topics.
Immigrant flows were larger in the past. This is true whether the flows are measured relative to the size of the resident population or to its growth rate.
Immigration around the turn of the century was dominated by single males of young working ages. Today's flows include many more women and children.
Many of the immigrants during the period of high immigration were sojourner workers who came to the United States to work for a few years and then return to their home country. Today's immigrants are far more likely to be reuniting with family members in this country or to be refugees. Far more than was ever true in the past, today's immigrants come to stay.
In the past, immigrant flows were highly responsive to economic conditions in the United States. The numbers swelled when the U.S. economy was booming, wages were rising, and unemployment was low. They ebbed when the economy was depressed. Emigration, the return flow, was highest during American depressions and was reduced during booms. Today the ebbs and flows over time are related to political —not economic—conditions. In particular, some of the largest annual flows in recent years occurred during periods of economic recession in the United States.
In the past, America selected people with above-average skills and backgrounds from their countries of origin. Today this pattern still holds for some sending countries, but is less clear for some others.