Just bumped into this paper via Kathy van Stone on the TDD list
http://www.cebase.org/www/frames.html?/www/researchActivities/defectReduction/top10/index.html
The summary (in garish yellow and red) is:
- Finding and fixing a software problem after delivery is often 100 times more expensive than finding and fixing it during the requirements and design phase.
- About 40-50% of the effort on current software projects is spent on avoidable rework.
- About 80% of the avoidable rework comes from 20% of the defects.
- About 80% of the defects come from 20% of the modules and about half the modules are defect free.
- About 90% of the downtime comes from at most 10% of the defects.
- Peer reviews catch 60% of the defects.
- Perspective-based reviews catch 35% more defects than non-directed reviews.
- Disciplined personal practices can reduce defect introduction rates by up to 75%.
- All other things being equal, it costs 50% more per source instruction to develop high-dependability software products than to develop low-dependability software products. However, the investment is more than worth it if significant operations and maintenance costs are involved.
- About 40-50% of user programs enter use with nontrivial defects.