Statistics of positive impact of TDD/BDD

Question

Everyone knows about some relevant statistics about positive impact of using test/behavior driven development in real projects. I know statistics can be very misleading, but it would be nice to see something like:

"when started using TDD, we rose productivity and reduced bugs introduction by XY %...".

It would be really nice to show this numbers to managers/customers, when explaining need of writing tests (there are still some people thinking we don't have time for this...)

Thanks

Answer 1

I have collected the following resources so far:

Realizing quality improvement through test driven development: results and experiences of four industrial teams (Microsoft Research):
http://research.microsoft.com/en-us/groups/ese/nagappan_tdd.pdf
resp:
http://www.springerlink.com/content/q91566748q234325/?p=7fd98b01480f49e2925f36393c999a72&pi=3

Test driven development: empirical body of evidence (ITEA):
http://www.agile-itea.org/public/deliverables/ITEA-AGILE-D2.7_v1.0.pdf

A Longitudinal Study of the Use of a Test-Driven Development Practice in Industry (IBM):
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.104.6319&rep=rep1&type=pdf

Evaluating Pair Programming with Respect to System Complexity and Programmer Expertise (IEEE):
http://simula.no/research/se/publications/Arisholm.2006.2/simula_pdf_file

There is a discussion on InfoQ:
http://www.infoq.com/news/2009/03/TDD-Improves-Quality

Also check out this question:
Evidence based studies on the topic of best programming practices?