- Year not given · 4 marks
Statistical SQA
Short answer
Statistical SQA quantitatively analyzes defect data, traces errors to underlying causes, and applies the Pareto principle to find the vital few. It corrects these causes and remeasures; Six Sigma's DMAIC is a widely used implementation.
Explain statistical SQA.
Statistical SQA is a quantitative approach to software quality assurance. Data about software defects is collected and analysed, and the few causes that produce most of the defects are found and corrected.
Steps (Pressman):
- Collect and categorize information about errors and defects from reviews, testing and field use.
- Trace each error to its underlying cause, such as incomplete or erroneous specification (IES), misinterpretation of customer communication (MCC), error in data representation (EDR), violation of programming standards (VPS), or incomplete testing (IET).
- Apply the Pareto principle: about 80% of defects come from about 20% of the causes. Isolate these "vital few" causes.
- Correct the problems behind the vital few causes by improving the process, then keep measuring.
Example
| Cause | Defects | % |
|---|---|---|
| IES | 90 | 30 |
| MCC | 60 | 20 |
| EDR | 45 | 15 |
| 9 other causes | 105 | 35 |
| Total | 300 | 100 |
Three causes produce 65% of the defects. The team therefore introduces SRS templates and reviews (for IES), prototypes shown to the customer (for MCC), and data-structure reviews (for EDR), instead of spreading effort over all twelve causes.
Six Sigma, the most widely used statistical quality strategy, follows the same idea with its DMAIC steps: Define, Measure, Analyze, Improve, Control.
✓ Answer checked by Claude Opus 5.5 (high effort)
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