Question: “Grammar Guy, I see the word ‘data’ used all the time as both a singular and plural noun. Can it be both, or is there a consistent rule for it?”
Answer: I’ve been saving this question for the right time, and since I’ve spent the last week nose-deep in spreadsheets, I think I’m ready for it.
To begin with, “data” comes to us directly from Latin, where it is the plural form of “datum” (Meaning: “an item given”). In English, we understand data as “facts or information used usually to calculate, analyze, or plan something.” When you enter your destination into MapQuest: That’s data. When you fill out a survey: That’s data. When you vote in an election: That’s data. Data is information.
Some professional organizations have endeavored to standardize the use of “data.” The American Psychological Association, which regulates APA Style, has, for example, decided that “data” is always to be used as a plural noun.
For most uses that don’t follow APA Style, however, you’ll need to decide whether “data” is acting as a count noun or a mass noun.
The best way to do this is to decide whether you are referring to individual units of data or an abstract group of data as a whole. A trick to help you figure this out at first is to mentally add the word “points” after “data” in the sentence and see whether it makes sense.
For example: “These data (points) are out of order” vs. “This data (points) comes to us from the CDC.” In the first sentence, the addition of “points” makes sense because we are talking about individual data. “Data” is therefore a count noun and should be treated as a plural. In the second sentence, adding “points” doesn’t make sense – “data” is acting as a mass noun and should get a singular verb.
Sometimes, though, treating “data” as a singular or plural noun comes down to personal preference. Consider this sentence: “Self-reported data (is/are) historically unreliable.” “Data” could be used as either a singular or plural noun in the sentence, and both choices would make sense and be grammatically acceptable. Like the data itself, how you use it is up to you.