Language skill definition: a study of legalized aliens

"The robustness of the model for the acquisition of destination language skills is studied using the Legalized Population Survey (LPS) of aliens who received amnesty under the 1986 [U.S.] Immigration Reform and Control Act. The English language proficiency variables include self-assessed overall speaking skills (the census question), speaking and reading skills in specific situations, perceptions as to whether language skills limit job opportunities, and measures of speaking and reading proficiency at work. The model is found to be robust across definitions of proficiency. Proficiency increases with exposure, efficiency and economic incentives for English language acquisition. The panel feature of the data is used to analyze changes in proficiency over time."