TDD

Phil Haack found a great paper published in the Proceedings of the IEEE Transactions on Software Engineering entitled On the Effectiveness of Test-first Approach to Programming. They end up concluding:

Our main result is that Test-First programmers write more tests per unit of programming effort. In turn, a higher number of programmer tests lead to proportionally higher levels of productivity.

[...]

Test-First programmers did not achieve better quality on average, although they achieved more consistent quality results. We attribute the latter observation to the influence of skill on quality, which Test-First tended to dampen.
Writing more tests improved the minimum quality achievable and decreased the variation, but this effect does not appear to be specific to Test-First.
In summary, the effectiveness of the Test-First technique might very well hinge on its ability to encourage programmers to back up their code with test assets. Future experiments could focus on this ability.

Strange as it may seem, the Test-First wasn't as important as the Test-a-Lot. I still feel the Test-First is of great importance, but then again I don't have a paper to back it, just unmeasured empirics.