Estimates of the number of illegal aliens: An analysis of the sources of disagreement

This article analyzes differences in estimates of the number of illegal aliens in the United States. Although smaller than differences among estimates made by some of the earlier studies, estimates constructed in the past decade often differ by several million. An examination of the problems involved in making these estimates produced four likely sources of the discrepancies. The four sources of disagreement are discussed, followed by suggestions for improving the reliability of the estimates. Some consequences for immigration law reform are also addressed.