Undocumented residents in the United States in 1990: issues of uncertainty in quantification

"Uncertainties are abundant about the measurement of net undocumented migration [to the United States] and change over the past two decades. This analysis presents possible upper and lower boundaries on components for estimating legal migration in 1980-1989 and on the foreign-born population in 1990. Positing ranges for net undocumented immigration, between 2 million and 4 million undocumented residents may have been counted in the 1990 census. The total number of undocumented residents may have been as high as 6 million."