"The word 'data'

is one of the most grammatically misused words in the English language. Why? Because most people use this word as though it were a singular word when it is, in fact, plural. Any time you read "the data is," you have found a grammatical error. Instead, when describing data, the phrasing should be "the data are." Get used to it: You are now one of the foot soldiers in the crusade to get people to use this word appropriately. It will be a long and uphill battle."
Kellstedt & Whitten. The Fundamentals of Political Science Research (79).

The singular is datum dayum!