Study of wealth ownership shows, however, that the Irish caught up to the Germans and the British by 1860, after controlling for changes in occupation and location. The relative economic position of all immigrants improved with length of time spent in the country. Ferrie suggests that with time immigrants were better able to match their skills with opportunities the American economy had to offer. Scholars have criticized community based studies of social and economic mobility for their possible biases in analyzing only those who persisted. The unskilled who left did no worse than those who remained behind.
Community based studies therefore underestimate the extent of upward and downward mobility.
If immigration had a substantial effect on natives, one would expect to notice the results during the high immigration rates of the mid-nineteenth century. Estimates of this model indicate that immigration lowered the incomes of skilled workers, but in contrast to other studies, the unskilled apparently benefited. They are difficult to follow in the original and will be indecipherable if reproduced on overheads. But this is nit picking in a book that gives us such novel and important results through extraordinary effort and ingenuity. Generations of students will compare this book against all others in the field of immigration history.