Data: plural or singular?
TLDR: Both, but you’d probably only use the mass noun singular version.
The word data is one that causes me a little bit of grief in my professional life. As an editor, I enjoy adding commas here and rearranging sentences there, but the inconsistent use of data in my office is causing me to go a little bit batty.
The main problem is that the word is in a transitionary phase, where some industries still cling to the dual-use origins of the word while the greater majority are beginning to drop its plural meaning.
data (count noun)—pieces of information, facts, statistics, assumptions or details that can be individually identified or counted; plural of datum
These data show the struggling condition of the processing plant.
Our data are supplied by the company reports.
data (mass noun)—collective information that cannot readily be counted; singular
There is no data on this company.
Much of this data is not reliable.
While the word datum is only still common in highly technical material, it and its plural data are not as commonly used as the singular mass noun data.
My work involves reading a lot of scientific and technical information (mostly involving geology and commodity manufacturing/processing); however, the writers of said information appear split on whether they should use one data or the other.
The best way to determine which to use is to replace data with another word. As the mass noun is singular, we can use information and is, has and much.
There is simply too much information to process all at once.
Whereas, for the plural data, we can replace this with facts and are, were and many.
Many of the facts were surprising.
However, whether you choose to use the plural data or the singular mass noun is entirely up to you—unless, of course, you are working with a style guide. Regardless, you must be consistent with whichever option you choose. I personally don’t like the sound of the plural data, but when I put my worker hat on, I try to forget about that!