quotes from http://research.microsoft.com/pubs/140711/ownership.pdf :
The results of our analysis of ownership in Windows Vista can be interpreted as follows:
1) The number of minor contributors has a strong positive relationship with both pre- and post-release failures even when controlling for metrics such as size, churn, and complexity.
2) Higher levels of ownership for the top contributor to a component results in fewer failures when controlling for the same metrics, but the effect is smaller than the number of minor contributors.
3) Ownership has a stronger relationship with pre-release failures than post-release failures