Quality Management
Quality on this exam is about processes, evidence, and prevention, not about inspecting defects out at the end.
Core rules
- Quality means conformance to requirements and fitness for use; grade is a category of features. Low grade can be planned and acceptable; low quality is not.
- Quality planning sets standards, metrics and acceptance criteria. Quality assurance audits the process. Quality control inspects the product and measures it against criteria.
- Cost of quality: prevention plus appraisal is the cost of conformance; internal plus external failure is the cost of nonconformance. Failure costs usually dominate, so prevention is cheaper.
- Tools: Pareto chart for the vital few causes, cause-and-effect diagram, histogram, control chart, scatter diagram, flowchart, check sheet.
- Control limits come from process data; specification limits come from the customer. A process can be statistically in control and still out of specification.
Worked example
A team logs 100 defects: 38 from unclear requirements, 24 from untested interfaces, 14 from environment mismatch, 24 from other causes. Pareto says fix requirements and interfaces first, which removes 62 percent of defects. Cost of quality: prevention 10k plus appraisal 15k plus internal failure 25k plus external failure 50k equals 100k, of which 75k is failure spend. Reasoning: shift investment toward prevention, then re-measure defect rates to prove the shift worked.
Traps
- Calling inspection quality assurance.
- Gold plating: unrequested features are defects, not generosity.
- Treating a control chart excursion as bad luck instead of a signal to investigate.
- Writing acceptance criteria after the work is finished.