PMP lesson · Quality · Quality · lesson 2 of 3 · about 8 minutes
Manage quality vs control quality (and control charts)
All approachesFree preview
Goal: After this lesson you can tell quality assurance from quality control, read a control chart, and apply the rule of seven.
1The situation
Everything is within limits… isn't it?
Two things happen in the same week. A quality audit finds that the welding team has been skipping the pre-weld checklist for six weeks. And the weld thickness chart shows the last seven samples all above the average, although every value is still inside the limits.
The production supervisor says: “No defects, all within limits: no problem.”
He is wrong twice. The first issue is about the process; the second is a pattern in the product data. Both need action.
2Process vs product
Quality management has two sides:
Manage quality
Process (assurance)
Are we following the quality plan, and is the process working? Audits, process improvement.
Control quality
Product (control)
Does this deliverable meet its specification? Inspection, testing, measurement.
Exam shortcut: audit, process, “are we following procedures?” → manage quality · inspect, measure, test the deliverable → control quality.
3A control chart with a warning
All points are inside the limits, but the last seven (red) are above the mean: the process has shifted.
4How it looks on the exam
Exam-style question 1. A control chart shows the last seven measurements above the mean, although all are within the control limits and within specification. The supervisor says no action is needed. What should the project manager do?
A. Agree, since all values are within limits
B. Treat the pattern as a sign that the process may be out of control and investigate the cause
C. Widen the control limits
D. Reject the last seven batches
Show the answer and the decode
Answer: B.
In simple English
Everything is within limits, but there is a run of seven on one side.
What is the question really asking?
Whether to act.
Key words / trigger
“last seven measurements above the mean”
PMP logic
Rule of seven: a non-random pattern suggests an assignable cause.
Why the wrong answer looks attractive
'Within limits' sounds conclusive, but patterns matter too.