Spanish language in the United States:

Calvin Veltman undertook, for the National Center for Education Statistics and for the Hispanic Policy Development Project, the most complete study of English language adoption by Hispanophone immigrants. Mr Veltman's language shift studies document high bilingualism rates and subsequent adoption of English as the preferred language of Hispanics, particularly by the young and the native-born. The complete set of these studies' demographic projections postulates the near-complete assimilation of a given Hispanophone immigrant cohort within two generations. Although his study based itself upon a large 1976 sample from the Bureau of the Census (which has not been repeated), data from the 1990 Census tend to confirm the great Anglicization of the US Hispanic American origin population.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Who undertook the most complete study of Hispanic language adoption?
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