Circular, invisible, and ambiguous migrants: Components of difference in estimates of the number of unauthorized Mexican migrants in the United States

Based on an equation that can be used with available data and that provides a basis for facilitating decomposition analyses, this research estimates t hat about 2.54 million total (as opposed to enumerated) unauthorized Mexica ns resided in the United States in 1996. Comparing this figure with an esti mate of about 2.70 million released by the U.S. Immigration and Naturalizat ion Service (INS) during the 1990s, we find that the two estimates involve different assumptions about circular invisible, and ambiguous migrants. Sti ch differences not only can have important policy implications; they can al so be sizable and can operate in opposite directions, as illustrated by fin dings from a components-of-difference analysis. The results are also extrap olated to 2000, and implications for 2000 census counts are discussed.