2 (9) U.S. Bureau of the Census, various years and countries, Country Demographic Profiles, (10) U.S. Committee for Refugees, recent years, World<sup>Refugee</sup> Survey, and (11) Refugee Reports and data from the United Nations High Commission for Refugees.

In some of these sources, the international migration assumptions are not stated explicitly or are buried in footnotes that<sup>do not always convey</sup> complete information. However, it is possible<sup>to obtain projections of</sup> international migration from multiple sources that are reasonably comparable.

The evaluation of international migration estimates and projections is hampered by problems of data coverage and quality, as<sup>well as definitional and</sup> methodological problems. As might be expected, the coverage of<sup>international</sup> migration statistics is quite spotty, the statistics<sup>are of variable quality,</sup> and there is little consensus on the future course<sup>of international</sup> migration flows. Migration statistics are generally collected for<sup>administrative</sup> purposes only (primarily with regard to the enforcement<sup>of immigration</sup> legislation) and little thought is given to their use for research<sup>or</sup> programmatic purposes. Although there have been United Nations recommendations on the collection of comparable international migration statistics since 1953 and other organizations such as the International Labor Office and the International Statistical Institute have made efforts to standardize international migration statistics, very few countries have chosen to design their own statistics to be consistent with<sup>international</sup> recommendations (Kraly and Gnanasekaran, 1987; Simmons, 1987; Kelly, 1987). In fact, a recent conference on international migration statistics concluded that the attainment of homogeneity in international migration statistics is not even a feasible goal at the current time (Zlotnick,<sup>1987b:1543).</sup> The World Bank's estimates and projections include as<sup>migrants primarily</sup> those persons who are likely to remain permanently<sup>in the receiving countries.</sup> In the principal receiving countries, the statistics<sup>on immigrants who are</sup> legally admitted for permanent residence are reasonably<sup>accurate. However,</sup> legal admission for permanent residence does not necessarily<sup>fit the World</sup> Bank's definition of permanent residence. For<sup>example, there are thousands of</sup> persons in such origin areas as Hong Kong, Korea,<sup>and Taiwan, who have</sup> received green cards for permanent residence in the<sup>United States, but who</sup> continue to live in their-home countries. They visit<sup>the U.S. only often</sup> enough to maintain the validity of their permanent<sup>residence cards. Although</sup> they maintain the ability to physically move to the United<sup>States at a later</sup> date should they choose to do so, they cannot<sup>be considered U.S. residents at</sup> the present time. Unfortunately, no precise estimates have been made of the extent of this phenomenon.

While statistics on legal immigration are adequate<sup>for most large</sup> receiving countries, two other components of net international migration are poorly measured -- emigration and illegal or undocumented migration. The largest destination country -- the United States -- has not<sup>collected any</sup>