Summary

In response to a congressional request, GAO reviewed methodologies used in measuring hidden populations for their potential in improving estimates of illegal aliens, described the problems attending the use of alternative estimation methods, and presented options for acquiring improved policymaking information in the illegal alien area.

Acquiring population statistics on illegal aliens is important, not only because of their illegal status, but also because illegal aliens are considered to be aggravating employment and community resource problems. However, available estimates of the size and growth of the illegal alien population are not satisfactory for policymaking. Accurate estimates of population size for other hidden populations have been made, but the prospects of using any of these methods to estimate the size of the illegal alien population are poor because knowledge is limited. Current estimates stem from incomplete or questionable databases or untested or demonstrably incorrect assumptions or are restricted to a subgroup of the illegal alien population. Producing reliable estimates from available methods would require an extensive, expensive, and time-consuming research program, although estimates of changes in both the size of the illegal alien population and its flow into the country may be sufficient for some policymaking purposes. GAO discussed another method that could yield accurate estimates of various subgroups of the illegal alien population. The usefulness and accuracy of such information depend upon the specific subgroup in question and have to be assessed carefully case by case. Estimating the illegal alien population as a whole requires more specific information than presently exists. Congress should weigh the extent of its concern for such information against the significant expenditures that would be necessary for its acquisition.