Mixing up quality assurance and quality control is one of the most common PMP mistakes. They sound alike, but they check different things. Here is the difference, the cost of quality, and the tools the exam expects you to recognise.
Three quality activities
| Activity | What it does | Focus |
|---|---|---|
| Plan quality | Decide the standards and metrics | Before the work |
| Manage quality (quality assurance, QA) | Audit the process so the standards will be met | Process |
| Control quality (QC) | Inspect the deliverables against the standards | Product |
The one-line rule: assurance checks the process, control checks the product.
Quick test: QA or QC?
- Auditing how the team does code reviews → QA
- Testing a batch of finished features → QC
- Using lessons learned to improve the testing process → QA
- Producing verified deliverables, ready for the customer's acceptance → QC
The cost of quality
PMI splits quality costs into two groups:
- Cost of conformance (money spent to get it right): prevention (training, standards, good design) and appraisal (testing, inspections, audits).
- Cost of nonconformance (money spent because it went wrong): internal failure (rework, scrap, found before the customer) and external failure (warranty claims, lost customers, damaged reputation).
The later a defect is found, the more it costs. That's why PMI's philosophy is prevention over inspection: build quality into the process instead of trying to inspect it in at the end.
The classic exam scenario
"Defects keep increasing before each release. Leadership wants to hire more testers." More testers is more inspection. The better answer is to find the root cause in the process, such as a skipped design review, and fix it. Fewer defects get made, which beats finding more of them.
The seven basic quality tools
- Cause-and-effect (fishbone) diagram: finds possible root causes.
- Pareto chart: ranks causes by frequency, so you fix the "vital few" first (the 80/20 rule).
- Control chart: shows whether a process is stable. A point outside the control limits, or seven points in a row on one side of the mean, means investigate.
- Check sheet, histogram, scatter diagram and flowchart complete the set.
Also know the difference between control limits (from the process) and specification limits (from the customer), and that adjusting a stable process after every point is tampering.
Learn it with visuals
The free chapter Plan and Optimize Quality has slides, a short video with animated fishbone, Pareto and control charts, and practice questions. Then test yourself on the free full PMP mock exam.