I just read Realizing quality improvement through test driven development. It’s a summary of 4 TDD teams at IBM and Microsoft compared to similar non TDD teams. With all the variables in any software project it’s hard to draw a hard conclusion, but this shows definite trends toward fewer defects minimal increased time, and I’d argue less time, because the reduced number of defects. I think the time measurement here is really subjective as it’s based on the judgment of the project managers. Regardless, I think these types of studies help prove the importance of good software practices.