Defect Metrics
Defect Metrics are quantitative measures used to analyze defects, assess product quality, and evaluate the effectiveness of the testing process.
Defect metrics answer: “What do defect numbers tell us about quality and risk?”
1. Definition
Defect Metrics are quantitative measures used to analyze defects, assess product quality, and evaluate the effectiveness of the testing process.
Defect metrics answer: “What do defect numbers tell us about quality and risk?”
2. Purpose of Defect Metrics
- Measure product quality objectively
- Track testing effectiveness
- Identify risk areas and trends
- Support release and go/no-go decisions
- Enable continuous process improvement
3. Key Defect Metrics (Manual Testing Focus)
3.1 Defect Density
Measures defects relative to size.
Formula: Defects / Size (modules, features, KLOC*)
Use:
- Compare quality across modules
- Identify defect-prone areas
3.2 Defect Severity Distribution
Shows defects by severity (Critical/High/Medium/Low).
Use:
- Assess business risk
- Focus fixing effort
3.3 Defect Priority Distribution
Shows urgency of fixes.
Use:
- Plan release timelines
- Allocate resources
3.4 Defect Leakage
Defects found after release.
Formula: (Production defects / Total defects) × 100
Use:
- Measure testing effectiveness
3.5 Defect Rejection Rate
Percentage of defects rejected (Not a bug, Duplicate).
Formula: (Rejected defects / Total reported) × 100
Use:
- Evaluate requirement clarity
- Improve defect reporting quality
3.6 Defect Removal Efficiency (DRE)
Effectiveness of defect removal before release.
Formula: Defects removed before release / Total defects × 100
Use:
- Assess quality control strength
3.7 Defect Aging
Time defects remain open.
Use:
- Identify process bottlenecks
- Improve turnaround time
4. Sample Defect Metrics Snapshot (Conceptual)
| Metric | Value |
|---|---|
| Total Defects | 120 |
| Critical Defects | 5 |
| Open Defects | 12 |
| Defect Leakage | 3% |
| Rejection Rate | 8% |
5. Manual Tester’s Role
- Log accurate defects
- Assign correct severity
- Update defect status timely
- Provide data for metrics
- Interpret metrics with context
6. Using Defect Metrics Effectively
- Analyze trends, not just numbers
- Combine with qualitative insights
- Avoid using metrics to blame individuals
- Use metrics to improve process
7. Common Misinterpretations
- More defects ≠ worse testers
- Fewer defects ≠ better quality (could mean poor testing)
- Metrics without context are misleading
8. Defect Metrics vs Test Metrics
| Aspect | Defect Metrics | Test Metrics |
|---|---|---|
| Focus | Defects | Test execution |
| Measure | Quality issues | Testing progress |
9. Interview-Ready Answers
Short answer:
Defect metrics are measurements used to evaluate software quality and testing effectiveness.
Detailed answer:
Defect metrics help teams analyze defect trends, severity, leakage, and removal efficiency to make informed quality and release decisions.
10. Key Takeaway
Defect Metrics provide data-driven insight into quality, but decisions require context and judgment.