John B. Bremner, in Words on Words, states unequivocally, "The word is plural." This one is thorny, because the singular, datum, is virtually nonexistent in English. Many people see data as a synonym for "information," and to them, These data are very interesting sounds downright bizarre. Maybe, but it's also correct. Theodore M. Bernstein, in The Careful Writer, says, "Some respected and learned writers have used data as a singular. But a great many more have not."