Typical Control Chart Guidance and Hypothesis

Steve Prevette

Deming Disciple
Staff member
Super Moderator
#11
One other thing (I'm sure you already know this). Traditional approaches to control charts is based on normality of data and bell curve. Steve bases his approach on... I'm not even going to attempt his name.. inequality. Not sure how detailed/deep you're going with this. If you're pushing to publish this, it might be worth mentioning.
Tchybychev, or Chebychev. Shewhart invoked Tchybychev. Duncan invoked both Tchybychev, and the Camp-Meidel extension. Deming invoked that it (SPC) is an empirical method that works.

It may also be worth noting that Dr. Shewhart tested his scheme with a 1930's random number generator - numbered hat tokens in a bowl. He made up three sets - normal, rectangular, and triangular distributions. The random numbers he ended up drawing are laboriously reprinted in Economic Control of Quality . . .
 
Elsmar Forum Sponsor

Stijloor

Staff member
Super Moderator
#12
Tchybychev, or Chebychev. Shewhart invoked Tchybychev. Duncan invoked both Tchybychev, and the Camp-Meidel extension. Deming invoked that it (SPC) is an empirical method that works.

It may also be worth noting that Dr. Shewhart tested his scheme with a 1930's random number generator - numbered hat tokens in a bowl. He made up three sets - normal, rectangular, and triangular distributions. The random numbers he ended up drawing are laboriously reprinted in Economic Control of Quality . . .
Hello,

For those who want to learn more about this remarkable person.

http://en.wikipedia.org/wiki/Pafnuty_Chebyshev

I found it very interesting...

Greetings.

Stijloor.
 

Tim Folkerts

Super Moderator
#13
Re: Control Chart Typical Guidance

Brad,

The construction guidelines came primarily from “Statistical Process Control”, Grant & Leavenworth as well as discussions with Steve and Tim Folkerts. I have discussed some of these techniques with Minitab because Minitab will not allow you to do control charts this way. For example, you cannot lock the control limits on Minitab. You can put a boundary on the limits, but you cannot lock them. Minitab and I are still talking, but they tell me they will look in to what I am telling them as a change to Minitab.
I'm away from Minitab for the next week, but I believe there is a way to do this. Buried within in the options for the chart, you can indicate which rows to use (or exclude) from calculations. If this works the way I think, then you could tell it to only use the first 25 points when calculating the limits. This might also prevent minitab from plotting the other points and performing the tests on them - in which case this wouldn't work.

You could also do the calculations after 25 and found out what the control limits are. I'm pretty sure there is a way to manually set the control limits, so you could just type in the numbers you found with 25 points. But that is not a very elegant solution.

Tim F
 
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