You can’t win with data. When you use it as a singular noun—e.g., this data is, which might sound more natural to nonscientists—you might lose credibility with some readers. When you use it as a plural noun—e.g., these data are—it might sound odd to readers who are used to hearing data as a singular noun.
In Latin, data is the plural of of datum, which means a thing given. But of course, data is an English word when English speakers use it, and we generally don’t let Latin hold sway over our language. The trouble with data is that it’s still relatively new to English—having emerged in its modern sense during the late 19th century—so we haven’t had much time to fully absorb it into English. Plus, data is a scientific word, and scientists are especially wont to honor Latin language conventions.
Outside science, fighting to preserve proper Latin grammar in modern English is a lost cause. The word is now well established in English, so we can think of it as an English word derived from Latin. In this case, we need not take Latin grammar rules into account. What matters now is how English speakers use the word, and a great many English speakers treat data as a mass noun. Mass nouns (e.g., love, water, courage, information) are usually treated as singular.
So, should we use data as singular or plural? It comes down to preference, and no English speaker can be faulted for using the one that sounds best (though no doubt some readers will vehemently disagree with us on this). But if you want to be safe, treat data as plural in scientific and academic contexts.
Examples
As these examples show, the word is used both ways in news publications:
Japan Economic Data Worsen [Wall Street Journal]
… by the time the data is published, copycat investors would have made an annualised loss of almost 10 per cent. [Financial Times]
Data are still being analyzed but will be ready to present at the conference. [Denver Post]
GDP Data Shows Japan’s Economic Growth Slowing [LA Times]
Obama’s campaign staff members said that all that data is not gathered to shape the message. [Washington Post]
Money data are not everything … [Telegraph]
