September 2001

Vol. 3, No. 9

Quality Quiz from Dr. Cleary

You're right!

Wanda's good intentions have indeed gone awry, violating Rule #2 of the "funnel experiment"  of W. Edwards Deming by adjusting the process to X-bar. This experiment demonstrated natural variability in a process by using a funnel to drop small beads on a target. If the funnel never moved, these beads would reflect variation, since no two would fall in exactly the same position.

If, on the other hand, the funnel is adjusted after each drop, the process would reflect increased variability. What Wanda is doing reflects Rule #2, "At drop k (k = 1,2,3.), the bead will come to rest at point  k, measured from target. Move the funnel distance - k from its last position." (See Deming, W. Edwards, Out of the Crisis (1982), Cambridge, MA: MIT Press.)

The funnel experiment is included on Quality Gamebox, which can be downloaded from

When you get to the funnel experiment, use Rule #1, with no adjustment in the process. Then go to Rule #2, which illustrates where Wanda went wrong. Tampering with a process can result in increasing the variability rather than diminishing it.

Copyright 2001 PQ Systems.

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