Process · Topic 9 of 12
Planning Quality
Plan and improve quality with cost of quality, the seven basic tools, control charts, audits and inspections, plus agile practices like done criteria.
- 4 min
- Quality means meeting requirements and being fit for use.
- Prevention is cheaper than inspection, and inspection is cheaper than failure.
- Cost of conformance has prevention and appraisal, and cost of nonconformance has internal and external failure.
What it is
Quality is the degree to which a product or deliverable meets its requirements and is fit for use. Quality management plans which standards apply, builds quality into the work, checks the results and improves the process. It supports both the customer's expectations and the organization's reputation.
A key principle is that prevention is cheaper than inspection, and inspection is cheaper than fixing defects after release.
How it works
Planning quality
Planning identifies the quality standards, the acceptance criteria and the metrics that will be used to measure results. A quality metric states exactly what is measured, such as defect density or response time. A quality management plan records who does what and when.
Quality is a requirement like any other, so it needs agreement from stakeholders early.
Cost of quality
Cost of quality adds up what the organization spends to get quality and what it loses when quality is poor.
| Category | Type | Examples |
|---|---|---|
| Cost of conformance | Prevention | Training, better design, process documentation |
| Cost of conformance | Appraisal | Inspection, testing, audits |
| Cost of nonconformance | Internal failure | Rework and scrap found before delivery |
| Cost of nonconformance | External failure | Warranty claims, returns, lost reputation |
Spending more on prevention generally lowers failure costs. External failures are usually the most expensive.
The seven basic quality tools
| Tool | Use |
|---|---|
| Cause and effect (fishbone, Ishikawa) diagram | Trace a problem to possible root causes |
| Flowchart | Show a process and find where problems enter |
| Check sheet | Collect data in a simple tally |
| Pareto chart | Rank causes by frequency to focus on the vital few |
| Histogram | Show the distribution of data |
| Control chart | Show whether a process is stable over time |
| Scatter diagram | Show a relationship between two variables |
A Pareto chart supports the idea that a small number of causes produces most of the problems, so fix those first.
Control charts and limits
A control chart plots results over time with a center line and upper and lower control limits, usually set at three standard deviations from the mean. A process within these limits is considered in control, and points outside them need investigation.
A run of seven consecutive points on one side of the mean suggests a non random pattern, even if all are inside the limits. Control limits describe the process, while specification limits come from the customer's requirements. They are not the same thing.
Managing and controlling quality
Manage quality focuses on the process. It uses audits to check whether the team follows the agreed processes, and root cause analysis to improve them.
Control quality focuses on the product. It uses inspection, testing and measurement to confirm that deliverables meet requirements.
Design of experiments changes several factors systematically to find the best combination. Benchmarking compares with other organizations. Both help to optimize quality.
Quality in agile and hybrid projects
Agile builds quality into every iteration. The definition of done sets a shared standard, and acceptance criteria describe when a story works.
Teams use automated tests, continuous integration, test driven development and frequent reviews to find defects early. Retrospectives improve the process.
Hybrid projects often apply formal standards and audits at the phase or release level, with agile quality practices inside each sprint.
When an exam question asks what a Pareto chart is for, remember it ranks causes by how often they occur, so effort goes to the biggest causes first.
What to remember for the exam
- Quality means meeting requirements and being fit for use.
- Prevention is cheaper than inspection, and inspection is cheaper than failure.
- Cost of conformance has prevention and appraisal, and cost of nonconformance has internal and external failure.
- The seven basic tools are cause and effect, flowchart, check sheet, Pareto, histogram, control chart and scatter diagram.
- Control limits describe the process, and specification limits describe customer requirements.
- Seven consecutive points on one side of the mean indicate a possible non random cause.
- Manage quality is about processes and audits, and control quality is about inspecting deliverables.
- Agile uses the definition of done, automated tests and retrospectives.
Common mistakes
Mixing up audit and inspection. An audit checks the process, and an inspection checks the product.
Confusing control and specification limits. A process can be stable but still outside what the customer wants.
Treating quality as the testers' job. Quality is a team responsibility, built in from the start.
Equating higher grade with higher quality. Grade is a category of features, and quality is how well requirements are met. A low grade product can be high quality.
Waiting for the end to test. Late defects cost much more than early ones.
Do not fix a defect and move on without finding the cause, because the same problem will recur.
Check yourself
Name the two parts of cost of conformance.
Prevention costs and appraisal costs.
What does a Pareto chart show?
Causes ranked by frequency, so the team can focus on the few causes that produce most defects.
What is the difference between manage quality and control quality?
Manage quality works on processes through audits and improvement, while control quality inspects and tests the deliverables.
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