As a followup to my previous post on gathering research information, I wanted to share the findings with everyone in case they're put in the same situation I (and another co-worker) was. Thanks to the strong efforts of my co-worker, we were able to produce good measurements of TDD effects.

Advantages of TDD:

• 87.5% of developers reported better requirements understanding.
• 95.8% of developers reported reduced debugging efforts.
• 78% of developers reported TDD improved overall productivity.
• 50% of developers found that it decreased overall development time.
• 92% of developers felt that TDD yielded high-quality code.
• 79% of developers believed TDD promoted simpler design.

The aggregate score of these findings shows that 80% of developers found TDD to be effective. Also, there was an increase in code quality which passed 18% more functional black-box tests.

Challenges of TDD:

• 40% of developers found adoption of TDD was difficult.
• 16% increase in development time of projets.

These results were of a survey done, and not scientific facts. It proved difficult to find statistics on TDD due to the "new" nature and adoption of TDD in the IT arena, which is why our results were based on surveys that were found across the internet.

References:

1. Elfriede, D. "Effective Software Testing: 50 Specific Ways to Improve your Testing"
2. Beck, K. "Test-Driven Development"
3. E. Michael Maximilien, "Assessing Test-Driven Development at IBM" Found Here.
4. George, B. and Williams, L., "An Initial Investigation of Test-Driven Development in Industry" Found Here.
5. "An Evaluation of Test-First in University Environment" Found Here.

Update: Some confusion about where we retrieved this numbers has come about. Our company did not do this survey, it was retrieved from one of the references stated in this article. I will talk with my co-worker, who found the survey, to give me specifics on which resource it was found at.

Update 2: After talking with my co-worker, she stated that the information I quoted above comes from the PDF found in reference #4. This was a study done over in Germany.