The number of illegal migrants of Mexican origin in the United States: sex ratio-based estimates for 1980.

This article reports the results of applying a sex ratio-based method to estimate the number of undocumented Mexicans residing in the United States in 1980. The approach centers on a comparison between the hypothetical sex ratio one would expect to find in Mexico in the absence of emigration to the United States and the sex ratio that is in fact reported in preliminary results from the 1980 Mexican Census. The procedure involves, inter alia, assuming a range of values for the sex ratio at birth and for census coverage differentials by sex in Mexico. Even the combinations of these values most likely to result in large estimates suggest that no more than 4 million illegal migrants of Mexican origin were residing in the United States in 1980.