Vol. 6, No. 3
from Professor Cleary
No. Simsack failed to tell his students about data patterns that indicate out-of-control situations even when data falls within control limits. The pattern reflected in this chart is statistically impossible if the process is truly in control. The sample p’s will form a normal distribution when the process is in control. But this chart reflects a number of points near the control limits and none around the average:
But virtually all of the points lie in the outer band—a pattern that could be caused by a variety of conditions, including some magic pencil that keeps things from getting out of control. Click to watch a demonstration of this out-of-control condition.
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