--- title: "SQA and statistical SQA" subject: "Software Engineering" chapter: 9 key: "semester_5/software_engineering:sqa-statistical" source: https://www.bctengineer.com/q/semester_5/software_engineering/sqa-statistical site: BCT Engineering --- # SQA and statistical SQA Software Engineering · Chapter 9: Quality management - Asked in: 2068 Baishakh (old course), 10 marks - Video: [Software Quality Assurance (SQA), Activities of SQA |SE|](https://www.youtube.com/watch?v=p8SYmtuJv10) — Trouble- Free - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/software_engineering/sqa-statistical - Whole chapter: https://www.bctengineer.com/md/semester_5/software_engineering/chapter-9 ## Question What is Software Quality Assurance (SQA)? What steps are required to perform Statistical SQA? ## Short answer SQA is planned systematic action ensuring software process and products conform to requirements, standards and procedures. Statistical SQA collects and categorizes defects, traces them to causes, applies the Pareto principle to isolate vital few causes, corrects them, then measures again. ## Answer #### Software Quality Assurance (SQA) **Software quality assurance** is a planned and systematic pattern of actions that ensures the software process and products conform to their requirements, standards and procedures. It is an umbrella activity that runs through the whole project. SQA includes (Pressman): - An SQA process and plan. - Quality assurance and control tasks: technical reviews and a multi-tiered testing strategy. - Effective software engineering methods and tools. - Control of work products and changes (configuration management). - Procedures to ensure compliance with standards. - Measurement and reporting. **Activities of the SQA group** - Prepare the SQA plan. - Take part in defining the project's software process. - Review engineering activities to check that they follow the defined process. - Audit designated work products. - Ensure deviations are documented and handled. - Record non-compliance and report it to senior management. #### Statistical SQA **Statistical SQA** is a quantitative approach to quality: information about defects is collected and analysed so that the team fixes the few causes that produce most of the defects, instead of reacting to individual bugs. **Steps** 1. **Collect and categorize** information about errors and defects found in reviews, testing and use. 2. **Trace each error to its underlying cause**, such as non-conformance to specification, design error, violation of standards, or poor communication with the customer. 3. **Apply the Pareto principle**: about 80% of defects come from about 20% of the possible causes. Isolate these "vital few" causes. 4. **Correct the vital few causes** by changing the process (training, better reviews, new tools), then measure again to confirm improvement. **Typical cause categories** | Code | Cause | |---|---| | IES | Incomplete or erroneous specifications | | MCC | Misinterpretation of customer communication | | IDS | Intentional deviation from specifications | | VPS | Violation of programming standards | | EDR | Error in data representation | | ICI | Inconsistent component interface | | EDL | Error in design logic | | IET | Incomplete or erroneous testing | | IID | Inaccurate or incomplete documentation | | PLT | Error in programming language translation of design | | HCI | Ambiguous or inconsistent human-computer interface | | MIS | Miscellaneous | **Example:** a team records 500 defects over one year. | Cause | Defects | % | |---|---|---| | IES | 110 | 22.0 | | MCC | 85 | 17.0 | | EDR | 70 | 14.0 | | IET | 55 | 11.0 | | ICI | 35 | 7.0 | | PLT, MIS (30 each) | 60 | 12.0 | | EDL, IDS, IID, VPS, HCI | 85 | 17.0 | | **Total** | **500** | **100** | IES, MCC and EDR are 3 of 12 causes but produce 265 defects (53%). Adding IET, 4 causes give 64%. So the team acts on these: - **IES**: use requirements templates and hold SRS reviews. - **MCC**: use prototyping and joint application meetings with the customer. - **EDR**: adopt data design tools and review data structures. - **IET**: improve test planning and coverage. ```text Collect defects --> Find causes --> Pareto analysis ^ | | v Measure again <-- Fix process <-- Vital few causes ``` **Six Sigma** extends statistical SQA. Its DMAIC steps are Define, Measure, Analyze, Improve, Control. The target is 3.4 defects per million occurrences. **Benefit:** effort goes where it gives the largest reduction in defects, and quality improves steadily over projects. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which description best fits Software Quality Assurance? A. Testing the finished product just before delivery B. A planned, systematic set of actions that runs through the whole project to ensure process and products conform to requirements and standards C. A one-time audit done by the customer after release D. Writing user documentation for the software Answer: B. SQA is an umbrella activity: planned and systematic, covering the whole project, not just final testing. (Key point: Meaning of SQA) 2. What is the main idea of statistical SQA? A. React to every individual bug as soon as it is reported B. Collect and analyse defect data to find and fix the few causes producing most defects C. Test every module equally with random data D. Measure only the number of lines of code written Answer: B. Statistical SQA is quantitative: defect data is analysed so effort goes to the few causes that produce most defects. (Key point: Idea of statistical SQA) 3. In statistical SQA, what does applying the Pareto principle mean? A. About 50% of defects come from 50% of causes, so all causes are fixed equally B. About 80% of defects come from about 20% of causes, so those vital few causes are isolated C. About 20% of defects come from 80% of causes, so most causes are ignored D. Every defect has exactly one cause and one fix Answer: B. Pareto: roughly 80% of defects arise from about 20% of causes; the 'vital few' are isolated and corrected first. (Key point: Pareto principle) 4. Which is the correct order of steps in statistical SQA? A. Apply Pareto, collect defects, trace causes, correct B. Correct causes, collect defects, apply Pareto, trace causes C. Collect and categorize defects, trace to causes, apply Pareto, correct vital few causes D. Trace causes, correct all causes, collect defects, measure Answer: C. Data is first collected, then traced to causes, then Pareto isolates the vital few, which are then corrected and re-measured. (Key point: Order of steps) ## Related in Software Engineering - [Software quality assurance](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Asqa-note) — Software Engineering, chapter 9 - [Statistical SQA](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Astatistical-sqa) — Software Engineering, chapter 9 - [SQA plan and quality standards](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Asqa-plan-standards) — Software Engineering, chapter 9 - [SQA plan](https://www.bctengineer.com/question.md?key=semester_5%2Fsoftware_engineering%3Asqa-plan) — Software Engineering, chapter 9 ## Related in other subjects - [Differentiate quality control and assurance](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aqa-vs-qc-differentiate) — Project Engineering, chapter 4 - [Quality assurance](https://www.bctengineer.com/question.md?key=semester_7%2Fict_project_management%3Aquality-assurance) — ICT Project Management, chapter 10 - [Quality; QA vs QC; site engineer steps](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aquality-qa-qc-site-engineer-steps) — Project Engineering, chapter 4 - [Steps to improve IT project quality](https://www.bctengineer.com/question.md?key=semester_7%2Fict_project_management%3Aimprove-it-project-quality) — ICT Project Management, chapter 10