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Gratton, B., and Myron Gutmann. 2000. "Hispanics in the United States 1850-1990: Estimates of Population Size and National Origin." Historical Methods, 33: 137-153.
Gratton and Gutmann present the first estimates based on representative data of the size of the Hispanic population of the US from 1850 to 1960. They also provide estimates of the size of each of the major Hispanic subgroups.