I think the time has come to abandon the concept of ‘data’ as a plural and to make it instead a singular collective term. To 99% of the population saying ‘The data in this study are conclusive’ just sounds clumsy, uncomfortable and, well, wrong. Make it ‘The data in this study is conclusive.’
It’s a bit like when I pour sugar from a spoon. I say ‘the sugar is falling into my cup’, because I’m referring to a collection of sugar crystals. Similarly, we can say ‘the data is’ rather than ‘the data are’ because we’re referring to a collection of data points.
Of course purists would argue that the word data is plural in Latin, so must be plural in English. Sorry, that’s outdated sophistry. It’s on a par with those who strangulate their sentences to carefully extract any split infinitives. (Sorry, sorry, I meant ‘carefully to extract any split infinitives.’) ‘But you can’t split an infinitive,’ they whine. ’It’s all one word in Latin.’ So what? I’m not writing Latin. Even Fowler thinks it’s a fuss over nothing.
Take a deep breath and write ‘this data is not suitable’ rather than ‘these data are not suitable’… or whatever. For the scientists among you, even if it comes hard, you will have taken one small step towards being able to interface better with human beings. For the rest of us, we can heave a sigh of relief and move on.