Responding to a commenter who used the phrase "this data," another commenter writes:
Not to be pedantic or anything, but I'm sure you meant these data. Perhaps it's old-fashioned, but I feel anyone with a PhD should be able to use "data" correctly. Anyone else, and I don't particularly care.
What puzzles me is what exactly the word "correctly" means here. My Merriam-Webster Webster's Dictionary of English Usage, for instance, reports that both the plural noun version of data (for which the dictionary offers the analogy earnings, and which takes plural verbs) and the abstract mass noun version (for which the dictionary offers the analogy information, and which takes singular verbs) "are standard" in English. In Latin, "data" might be exclusively plural. But we're speaking English, and in English both the singular and the plural are, according to this dictionary, fine.
My New Shorter Oxford likewise describes "data" as "pl. & collect. sing." The big online Oxford lists both. The American Heritage lists it as "pl. n. (used with a sing. or pl. verb)"; it does provide a usage note, but reports that "Sixty percent of the Usage Pannel accepts the use of data with a singular verb" as in "the data is in."
Garner's Dictionary of Modern American Usage is the most pro-plural modern source of the ones I've checked, but even it reports only that "in more or less formal contexts [data] is preferably treated as a plural." The original 1926 Fowler does insist that "data is plural only"; the 1996 New Fowler's Modern English Usage begins by giving as an example that "The data are (not is) insufficient," but reports that "In modern times usage varies," and notes that "In computing and allied disciplines [data] is treated as a singular noun."
Now let's set aside whether one views the singular data as elegant or grating; let's also set aside whether one would counsel one's students to take the course that will annoy, rightly or wrongly, the fewest readers. (Note that here both the singular and the plural versions may annoy some.) The claim was that the singular is not "correct." And I don't quite see for what sensible meaning of "correct" that claim is correct.