# **1. Introduction**

Economists have become increasingly cognizant of the importance of international migration over the last few years. In developed countries there has been intense debate about appropriate immigration policies (e.g Borjas, 2003), while among development economists interest has focused on the links between migration and development (e.g. Lucas, 2005, Ozden and Schiff, 2005). Topics include the determinants of migration (e.g. Hatton and Williamson, 2002), the role of migration and remittances in poverty alleviation (Ozden and Schiff, 2005, Part I), migration and human development (e.g. McKenzie and Rapoport, 2005, McKenzie and Hildebrandt, 2005), the brain drain (Stark, 2003, Commander, Kangasniemi and Winters, 2004, Docquier and Marfouk, 2005), SouthSouth migration (e.g. Ratha, 2006) and the links between migration, trade and investment (Rauch, 2001). At a global level, research has explored the benefits from possible agreements to foster South-North migration (Walmsley and Winters, 2005, Pritchett, 2006).

Given this increasing interest in migration, it might seem surprising that few attempts have been made to take a global view of the patterns of international migration between countries and regions. This deficiency essentially reflects the lack of comprehensive and reliable data on bilateral flows of migration. OECD produces detailed stock and flow data on immigrants in OECD and a few other countries (e.g. OECD, 2002), early versions of which have been used for analysis – e.g Mayda (2006). The United Nations adopts a global perspective when summarizing international migrant movements, but its work provides only total migrant stocks for each country. National data sources frequently allow some geographical disaggregation, but attempts to combine them into a broader framework exhibit a number of common failings: for example, data availability only for a particular region and serious challenges of comparability from one country to another. Among the latter is the problem of how to define migrants by place of origin. This can most readily be done either by country of birth or by country of citizenship, but where attempts have been made, typically no distinction is drawn between the two concepts despite the large disparities that exist between them.

This paper makes a start toward rectifying these shortcomings of the data by introducing four versions of two origin-destination matrices for 226 countries and territories using the data from the 2000 round of censuses.<sup>1</sup> The first of these matrices records foreign population by country of birth and the second the population by nationality, which, for the purposes of the paper, is treated as analogous to citizenship.<sup>2</sup> Though countries employ many different methods for collecting and presenting these data, we attempt to reconcile these methods to create as full and comparable a dataset as possible. The four versions reflect different points on the trade-off between the comprehensiveness of coverage and the use of assumption and interpolation to compensate for missing data. We report all four because the different versions will be appropriate for different uses, and we discuss

> 1 For reasons of space, the matrices cannot be reproduced in this paper. The first two versions are available on the website of the Development Research Centre on Migration, Globalisation and Poverty at www.migrationdrc.org/research/typesofmigration/global_migrant_origin_database.html The other two versions are available to researchers by request to the same centre or Version 4c only, aggregated to a 87x87 matrix, is available at: www.gtap.agecon.purdue.edu/models/labor_migration.asp

> 2 United Nations (1980) defines a person’s citizenship as their legal nationality. Following from this, no distinction is made here between citizenship and nationality, and thus no notion of belonging or of political or legal participation is employed.

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