Technically, “this data” and “these data” are both correct. But, such a thing wasn’t always the case. There’s a history of the word “data” in and of itself that isn’t an English word and actually falls under the grammatical rules of Latin. But, in the modern era, both versions are correct.
Therefore, the difference between the two phrases should be easy for newcomers. All you have to remember, though, is if you’re speaking about data that encompasses many items or just a single piece of data. This is so you can use proper numerical agreement rules.
The word “data” is actually the plural version of “datum,” a Latin word that means metrics, demographics, statistics, or other factual information used to base one’s discussion, argument, debate, reasoning, or other types of calculation.
For many years, correct English grammar determined that “data” have the same usage for rules of plurality. But, with the innovation of computers and the worldwide web, “data” has become an uncountable noun.
An uncountable noun is a word that can’t take on a numerical value to quantify itself. This isn’t only true for “data” but this also includes “food,” “money,” “information” and others. For instance, you wouldn’t write “there are seven data.” But, you might say, “there are seven data points.”
While you could use the first statement and it would be correct, it doesn’t sound right. Including “points” clarifies the kind of data you’re referring to.
Examples for Reference
The examples below show how both “this data” and “these data” can both be correct. However, if you feel sketchy or out of place when you need to use it, stay with the plural “these data.”
This data is true and factual.
These data are true and factual.
He says this data was shaky at best.
He says these data were shaky at best.
Check to see if this data has finished calculating.
Check to see if these data have finished calculating.
While it’s correct to use both “this data” and “these data,” “data” is essentially a plural word. So, if you want to stay sure of things, use “these data are.” But, if you’re speaking to people or giving a presentation, then using the singular form of “this data” will be better for the sake of comprehension. But, ensure the verb usage shares agreement.