destination country government has implemented them. In most continental European countries, family reuni...cation is the main route for many potential migrants. Even in one of the most selective country such as Canada, about 40 percent of immigrants come under the family reuni...cation and refugee programs, rather than selective employment or skill-based programs. Emegwali’s quotation perfectly illustrates these channels. Through network e¤ects (“our presence [. . . ] inspired our friends to immigrate here”) and family reuni...cation programs (“I became eligible to sponsor 35 relatives for a Green Card”), existing diasporas positively impact future ‡ows of migrants.

Only a few papers analyze the linkages between diasporas and the structure of migration ‡ows. Building on Chiquiar and Hanson (2005), Mc Kenzie and Rapoport (2007) start from the intermediate selection case (which re‡ects the Mexico-to-US pattern) and demonstrate that a decrease in migration costs generally has a stronger e¤ect on low-skill migration than on high-skilled migration.<sup>3</sup> Using survey data from Mexico, they show that the probability of migration increases with education in communities with low migrant networks, but decreasing with education in communities with high migrant networks. Taking advantage of a recent data set on international migration by educational attainment (see Docquier, Lowell and Marfouk, 2009), our paper generalizes this result by analyzing the role of diaspora size on the educational structure of migration from 195 countries to the 30 OECD countries. Accounting for the usual determinants of migration and correcting for several econometric problems, we show that larger diasporas increase migration ‡ows and lower their average educational level, as expected. To reinforce this result, we analyze the e¤ect of diasporas on the geographic concentration of high-skill and low-skill migrants. We show that diasporas increase the concentration of low-skill migrants relative to high-skilled ones.

Interestingly, diasporas explain a large portion of the variability of migrants’‡ows (71 percent) and selection (47 percent). These percentages capture both network externalities that lower migration costs and the e¤ect of family reuni...cation programs. Thus, without changing the generosity of these family reunion programs, educationbased migrant selection rules are likely to have a moderate impact,especially in countries hosting large diasporas. These results are highly robust to various econometric techniques, accounting for the large proportion of zeros and possible correlation of the network size with unobservable components of the migration ‡ows.

The remainder of the paper is organized as following. Section 2 describes migration data and presents some stylized facts on the size and structure of diaspora and migration ‡ows. Section 3 derives testable predictions from a stylized theoretical model. Econometric issues and empirical results are presented in Sections 4 and 5. Finally, Section 6 concludes.

> 3Bertolini (2009) provides also similar evidence from the Ecuadorian migration to Spain and the US. The negative selection of Ecuadorian migrants to the US is largely explained by the size of the networks at destination.

4