The calculation process:
Find all versions that were already released For each version, find all defects that affected the version. If defect creation date is after version release date then this defect is an escaped defect. Now count all those escaped defects.
Best Practices
Metric helps in tracking that sends correct message to development team:
Functionality that is released, should be of good quality
Less Escaped Defects almost always means good job of QA team
Best Practices that one should follow while analysis are:
Measure outcomes, not outputs
Measure results, not activity
Measure work items done, not time spent per task
Provides fuel for meaningful conversation May measure Value (Product) or Process
Encourages "good-enough" quality