We explore the self-selection of Mexican migrants to the United States in 1920. We hand-collect data for migrants from manifest lists for towns along the United States-Mexico border. Officials recorded the heights of migrants, a measure that we use to proxy migrant quality and measure self-selection into migration. Migrants, despite being relatively more unskilled than stayers, came from the middle to upper portion of the height distribution in Mexico, and so were positively selected. The result holds within skill group, suggesting that the United States received the best unskilled, skilled and professional workers.
In the conclusions, they add
Mexican migrants were over four centimeters taller than members of the Mexican military and only one and a half centimeters shorter than passport holders. Since the military drew from lower classes of Mexican society and the passport holders were elite, the fact that migrants were taller than those in the military and nearly as tall as passport holders tells us that they were positively selected from the Mexican population.