Defect Removal Efficiency will indicate the effectiveness of the defect identification and removal.
Defect Removal Efficiency shows how useful or effective quality management activities are on a phase-by-phase basis.
Defect Removal Efficiency can indicate if there are issues in the quality management system that needs correction. It can be used to manage quality throughout the software life cycle.
Defect Removal Efficiency can be used as a measure to set process and product improvement goals. For instance if the Defect Removal Efficiency for testing is 30 %, you may want to introduce new people, processes and tools to increase it to 40, 50 or even 75%.
Defect Removal Efficiency is a method to analyze the effectiveness of individual processes, especially appraisal processes like review, testing etc.
Defect Removal Efficiency - Example 1
W h e r e F r o m | Origin of Defect | ||||
|---|---|---|---|---|---|
| - | Requirement | Design | Code | Total | |
| Requirement Review | 15 | - | - | 15 | |
| Design Review | 5 | 29 | - | 34 | |
| Code Review | 1 | 3 | 54 | 58 | |
| Unit Testing | 0 | 4 | 32 | 36 | |
| Integration Testing | 1 | 3 | 13 | 17 | |
| System Testing | 2 | 0 | 6 | 8 | |
| Operations | 1 | 2 | 7 | 10 | |
| Total | 25 | 41 | 112 | ||
From the above table it should be clear that for the requirements phase, 15 requirement type defects were found and fixed during that phase and 10 requirement type defects were found in later phases for a total of 25 requirement type defects. For design phase, 29 design type defects were found and fixed during that phase and 12 design type defects were found in later phases for a total of 41 design type defects and so on.
Requirements Review Effectiveness:
Defects Removed at Requirements Review phase: 15
Defects existing on step entry: 0
Defects injected in the current phase: 25
(15/25) x 100 = 60%
Design Review Effectiveness:
Defects Removed at Design Review phase: 34
Defects existing on step entry (escapes from Requirements phase):
25 – 15 (these 15 already removed in requirements phase) = 10
Defects injected in the current phase: 41
(34/(41+10)) x 100 = 67%
Code Review Effectiveness:
Defects Removed at Code Review phase: 58
Defects existing on step entry (escapes from Requirements & Design phase):
25 +41-34-15=17
Defects injected in the current phase: 112
(58/17+112) x 100 = 45%
For testing phases, the defect injection is usually a smaller number, in such cases efficiency is calculated by a different method:
Unit Testing Effectiveness:
36/(36+17+8+10) X 100 = 51%
Integration Testing Effectiveness:
17/(17+8+10) X 100 = 49%
And so on.....
Defect Removal Efficiency - Example 2
Similar to table in example 1, below is another table of defects:
W h e r e F o u n d | Defect Origin | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Req | HL Design | LL Design | Code | Unit Testing | Component Testing | System Testing | Field | Total | ||
| RQ | - | - | - | - | - | - | - | - | - | |
| HL | 49 | 681 | - | - | - | - | - | - | 730 | |
| LL | 6 | 42 | 681 | - | - | - | - | - | 729 | |
| CR | 12 | 28 | 114 | 941 | - | - | - | 1095 | ||
| UT | 21 | 43 | 43 | 223 | 2 | - | - | - | 332 | |
| CT | 20 | 41 | 61 | 261 | - | 4 | - | - | 387 | |
| ST | 6 | 8 | 24 | 72 | - | - | 1 | - | 111 | |
| Field | 8 | 16 | 16 | 40 | - | - | - | 1 | 61 | |
| Total | 122 | 859 | 939 | 1537 | 2 | 4 | 1 | 1 | 3465 | |
High Level Design Inspection Effectiveness:
Defects Removed at High Level Design phase: 730
Defects existing on step entry (escapes from Requirements phase):122
Defects injected in the current phase: 859
(730/122+859) x 100 = 74%
Low Level Design Inspection Effectiveness:
Defects Removed at Low Level Design phase: 729
Defects existing on step entry (escapes from Requirements phase & High Level Design):
122 + 859 – 730 =251
Defects injected in the current phase: 939
(729/251+939) x 100 = 61%
As in the above example
Unit Testing Effectiveness:
332/(332+387+111+81) X 100 = 36%
Overall Inspection Effectiveness:
730+729+1095/122+859+939+1537 = 74%
And so on...
References:
[Software Testing and Quality Assurance, Publisher Nirali Prakashan]
[The Certified Software Quality Engineer Handbook By Linda Westfall]
Some more worth reading documents on Defect Removal Efficiency:
1. Defect Removal Efficiency calculator
DRE Calculator
2. Defect Removal Effectiveness
DRE Effectiveness
3. Measuring Defect Removal Efficiency
Measuring DRE
4. Enhancing Defect Removal Efficiency (DRE) using Adoption Rate for Released Products
Enhancing Defect Removal Efficiency
5. DRE, its purpose, how to calculate Defect Removal Efficiency etc
Defect Removal Efficiency
Also See:
Defect Density
Test Coverage
Test Effectiveness
Schedule Variance & Cost Variance
Effort Variance