Is the entry for 'please explain' usually "it's just common cause variation, dude"?

I have a target of four red beads. I know that 20% of the beads in the box are red. When I drew out 50 beads I got 14 red, even though I know the system should produce an average around 10. How do I word my explanation? I can't ask Deming. He's dead.

Hi Keith,

Your first question:

Most likely "it's just common cause variation" would not be an acceptable explanation, since if a process is under control, or has predictable variation due to chance or common cause, the "target" should allow for this. If your target is zero variation, and if this is a serious target, you may say "it's common cause variation" but not use the word "just," which implies that you are excused you from further analysis.

Your second question:

I'm not sure this is an appropriate analogy to the hour by hour chart since the target is based on an expected output over a period of time, and the "please explain" is addressing variation during that period. If your target is 4 red beads, why did you draw out 14?

If you do have a process with chance (common cause) variation to this degree, you don't have a stable process and you should stop measuring hour by hour and start working controlling and stabilizing it.

Unless we're talking about quantum level processes, I think we can say that this is not common cause variation but special cause variation.

If so, there would have been an error in the man, material, method, machine, measure or mother nature elements resulting in more than 20% of the beads being red in the box.

The explanation would require investigation by going to the workplace, opening the box, interviewing the worker, observing the method, calling the supplier, etc.

We can't ask Deming, but he left plenty of students you could ask.

There's something wrong with the reasoning here. The point of the Red Bead Experiment is to show that you cannot reduce process mean or it's standard deviation without remove the cause of the variation, which is the read beads. If you got only two red beads, would you have improved the process? Of course not. Since 20% of the beads are red, you're going to get a draw of none and a draw of 20% from time to time. Translated into real world terms, the common cause may be poor tooling, poor equipment, poor materials, etc. A special cause would be a broken tool, the wrong material, machine break-down, etc.

A second point, the target is not 4 red beads, it's 0 red beads, another reason the experiment is so frustrating. To get 0, you need also a special cause, which in this case, may be just dumb luck.

I have an automotive assembly line and it contains six different stations. The vehicles are on a automated line that has the speed controlled according to the fixed takt time. If an andon is hit the whole line stops. How do I use an hour by hour chart to expose the reasons for the line stoppages????

Our 'Hourly Production Tracking Sheet" showed us significant variation in throughput time due the following reasons:
1. Skid Prep Paper Work
2. Material Replenishment (Waiting for a fork truck)

Anybody with similar issues?
Regards,

Venkatesh