It isn't terribly clear from the abstract and I'm not going to pay for the paper, but it sounds like this is really a comparison of tests vs no tests. That has nothing to say about the practice of TDD.

This is why this newer study is interesting; it compares to TLD, which allows you to say something about TDD rather than just about testing.

Careful: sometimes even widely cited studies like Nagappan don't actually show what they are misreported as showing either. For example, if you look at the development processes being compared in the cases examined, often they aren't quite TDD as widely described and advocated.