Is ‘data’ singular or plural? In academic (particularly scientific) writing, it’s standard to see ‘these data are’. But otherwise, it’s increasingly common to see ‘this data is’. The question is whether we treat ‘data’ as meaning ‘distinct pieces of information’ or just ‘information’ (a grammatically singular mass noun).
Simon Rogers has a nice summary of the debate.
The academic usage follows tradition – and the word’s Latin origin, because of course ‘data’ is the Latin plural of ‘datum’. Case closed?
No: many linguists now believe that English is not Latin.
English has a lot of words taken directly from other languages, but that doesn’t mean that those words, as English words, need to follow the conventions of the original language. We lifted ‘schadenfreude’ and ‘dachshund’ from German, but we don’t give them the initial capitals that German nouns get.
For ‘data’, I think the best analogy is ‘news’. I watched the BBC’s fine adaptation of Henry IV Part 1 last night, and my ears pricked up when Jeremy Irons (in the title role) asked:
But wherefore do I tell these news to thee?
It turns out that when ‘news’ was first recorded, in the late 14th century, it was a plural – meaning ‘new things’. Over time, it came to be treated as singular, although as late as the 19th century there were still a few occurrences of ‘these news’. But plural ‘news’ sounds utterly alien to modern ears.
To most non-academics, plural ‘data’ isn’t there yet, but it does sound a bit odd and stuffy. It’s on its way out; in many areas of English, it’s already left.
So judge your audience: if writing in the kind of niche where plural ‘data’ remains the norm, you’ll probably do best to match their style. But otherwise, more of your readers will find ‘these data are’ peculiarly technical than will find ‘this data is’ depressingly illiterate.