record immigrants when they achieve their resident status rather than when they ...rst enter the country. Finally, de...nition of migrants - by nationality or birth - vary across countries. Most importantly for our purposes, those data are not available by education level. The ‡ows of immigrants to a country can only be recovered by measuring the stock of foreign born people in a destination country (from a certain origin country) at di¤erent points in time and then taking the di¤erence. The other advantage of starting with data on stocks of migrants is that they are usually from national censuses which tend to be more representative and complete than other data sources. Plus censuses often account for (i) undocumented immigrants at least in some countries like the US, (ii) they categorize immigrants by place of birth, rather than nationality which can change over time and across countries due to naturalization laws and (iii) report their education levels.

Our database is described in Docquier et al. (2010) who construct bilateral measures of immigrant and emigrant stocks for 195 countries in 1990 and 2000. The starting point for the new data is Docquier and Marfouk (2005) which collected the stock of foreign-born in OECD destination countries in 1990 and 2000, by country of origin and level of schooling (primary, secondary and tertiary). These data are supplemented with original data from the censuses of a large number of non-OECD countries. Finally, for many destination countries with no data on immigration, bilateral migrant stocks were predicted using a gravity framework as described in greater detail in Docquier et al. (2010). Their own census data would su¢ ce to measure immigration into OECD countries. However, evaluation of emigration also requires data from all the possible destination countries, at least the most relevant ones. In other words, emigrant stocks from a certain origin can only be measured by aggregating all migrants recorded in the censuses of all destination countries. As some important destination countries (such as Russia, South Africa, Brazil, Argentina, and Singapore) are outside the OECD, this new database ensures the coverage of essentially all emigrants from all countries in our sample. Table A2 in the appendix show that the majority of emigrants from Western Europe are in destination countries for which we have actual census data.<sup>6</sup> For most OECD countries, less than 10% of their emigrants are in countries with imputed (rather than actual) migration data. The only European country relying on imputed data for a large fraction of its emigrants is France at about 30%.

We distinguish two skill types s, denoted by s = h for college graduates (referred to as highly educated) and s = l for individuals with secondary education completed and less (referred to as less educated). The database covers the years 1990 and 2000 and the di¤erences in stocks by country of origin and destination provides the measures of the ‡ows. It focuses on individuals aged 25 and over as a proxy of the working-age labor force which is one of the main di¤erences with other migration databases (such as Ozden et al. 2010). This choice maximizes comparability between data on migration and on labor force per education attainment. Furthermore, it excludes a large number of students who emigrate temporarily to complete their education or children who migrate with their families.<sup>7</sup> The data description and some summary statistics follow.

> 6This pattern is also con...rmed in Ozden et.al. (2010) which presents global bilateral migration stocks but does not disaggregate by education levels.

> 7The dataset contains 195 source countries: 190 UN member states (after excluding North Korea), the Holy See, Taiwan, Hong Kong, Macao, and the Palestinian Territories. We consider the same set of countries in 1990 and 2000, although some of them had no legal existence in 1990.

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