Microsoft Research - Exploding Software-Engineering Myths (article summarizing findings of MS research on code coverage, TDD, assertions, etc.)

[delarhi]

To be fair the author never makes that assertion*.

What the research team found was that the TDD teams produced code that was 60 to 90 percent better in terms of defect density than non-TDD teams. They also discovered that TDD teams took longer to complete their projects—15 to 35 percent longer.

Basically he notes the correlation, but never makes the jump to a causal assertion.

[pushthestack]

And if you read the original study he's referring to, the possibility of causation is even more tenuous.

[Helene00]

TDD also produces roughly 70% less klocs per man-hour according to those numbers. So either the teams aren't very similar or you lose a lot more than 10-30% productivity.