PK0-005 Tools and Documentation Practice Question
A control chart shows a process with data points fluctuating within the upper and lower control limits, but 8 consecutive points appear on one side of the mean. What does this indicate?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Special cause variation
In a control chart, 8 consecutive points on one side of the mean (a 'run' of 8) indicates a special cause variation, even if points are within control limits. This rule is a common test for special causes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Common cause variation
Why it's wrong here
Common cause variation is random and within limits, but a run of 8 suggests a pattern.
- ✗
The mean has shifted
Why it's wrong here
A shift might occur, but the specific rule of 8 points is for special cause detection.
- ✗
The process is out of control
Why it's wrong here
The process may still be statistically in control if points are within limits, but a run of 8 is a warning sign.
- ✓
Special cause variation
Why this is correct
Correct. A long run indicates a non-random pattern, meaning special cause may be present.
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Written by Johnson Ajibi, MSc IT Security
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