Defect Removal Efficiency (DRE) is calculated as $DRE = rac{E}{E + D}$, where $E$ is defects found before release and $D$ is:
ATotal test cases executed
BLines of code written
CDefects found by customers after release
DTotal development hours spent
Explanation
DRE calculates the percentage of total defects caught by QA internal testing prior to production release.

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