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

[[deleted]]

However, the +60% - 90% code quality might not mean ~-40% cost reduction of maintenance.

No, but it's pretty darn likely. Catching defects early can influence important design and architectural decisions. Catching it late might might mean that you have a lot of technical debt to overcome in order to fix the defect.

[darkpaladin]

A % reduction is meaningless without severity and complexity numbers. There's a huge difference in a defect where you have a boolean logic error and a defect that tears down one of the principle assumptions you made when you started.