topic Cauchy distribution. Where is Process capability button? in Discussions

Cauchy distribution. Where is Process capability button?

Leonard — Sat, 10 Jun 2023 23:17:38 GMT

Why where is no Process Capability button? Or you can't do it with Cauchy's distribution data.

Re: Cauchy distribution. Where is Process capability button?

Leonard — Wed, 12 Aug 2020 12:28:53 GMT

Sorry... Why is there no process capability button?

Re: Cauchy distribution. Where is Process capability button?

txnelson — Wed, 12 Aug 2020 12:58:53 GMT

According to the JMP Documentation, the Cauchy distribution has an undefined Mean and Standard Deviation. Based upon that, I assume JMP does not have Cp and Cpk for that distribution and thus no need for the button.

Re: Cauchy distribution. Where is Process capability button?

Leonard — Wed, 12 Aug 2020 13:33:15 GMT

Yes, but then how do I calculate PPK? Should I take the nearest distribution, if it is? Or should I calculate PPK using Standard Deviation? I need to evaluate the process with nonnormal data distribution.

Re: Cauchy distribution. Where is Process capability button?

txnelson — Wed, 12 Aug 2020 13:41:22 GMT

Have you tried fitting all the Distributions, and then determine which have a significant Goodness Of Fit? You could then use that distribution for your Cp and Cpk

Re: Cauchy distribution. Where is Process capability button?

Leonard — Wed, 12 Aug 2020 14:05:23 GMT

yes I click Fit all

And recieve only three, where Cauchy has a priority.

Re: Cauchy distribution. Where is Process capability button?

txnelson — Wed, 12 Aug 2020 14:13:25 GMT

Check out the other fits.....they might give you good estimates

Re: Cauchy distribution. Where is Process capability button?

Leonard — Wed, 12 Aug 2020 14:24:58 GMT

but goodness of fit points to Cauchy

Re: Cauchy distribution. Where is Process capability button?

Mark_Bailey — Wed, 12 Aug 2020 18:01:07 GMT

Actually, the mean of the Cauchy distribution is defined but not the higher moments. So, no variance, no standard deviation. No standard deviation, no Ppk.

Re: Cauchy distribution. Where is Process capability button?

Kevin_Anderson — Wed, 12 Aug 2020 22:01:37 GMT

And, just as an aside, if you're responsible for improving a process that outputs data that are really Cauchy distributed, you might want to update your resume...

Re: Cauchy distribution. Where is Process capability button?

shampton82 — Thu, 13 Aug 2020 03:32:24 GMT

Is this count data? If so a couple of ideas: You could turn it into pass/fail based upon your defect limit then convert your defect rate to a Ppk from a sigma-DPMO-Ppk table. You could also fit it as Poisson and use the distribution profiler to determine what your DPMO rate was (by setting the x axis to your spec limit and using the returned Y value) and convert that into a Ppk. The other option would be to turn your zero's into 0.0001's and then you'll have some additional distributions you can fit.