topic Re: “Out of spec rate” calculation in Discussions

“Out of spec rate” calculation

MFellermann — Wed, 21 May 2025 10:03:55 GMT

Dear JMP community,

How is the “Out of spec rate” calculated in JMP (see image below)? The tool can be found in the evaluation of Ppk and Cpk values.

In JMP there are no formulas provided for the “Out of spec rate” calculation.

Is this based on an assumed normal distribution and the spec limits?

Thank you in advance.

Best regards
Maximilian

Re: “Out of spec rate” calculation

jthi — Wed, 21 May 2025 10:14:31 GMT

Quality and Process Methods > Process Screening > The Process Screening Report

Out of Spec Rate

The proportion of observations that fall outside the specification limits. On by default.

Re: “Out of spec rate” calculation

MFellermann — Wed, 21 May 2025 11:07:50 GMT

Thank you for the quick reply and your help. Does the program assume a normal distribution for calculating the proportions?

Thank you in advance.

Re: “Out of spec rate” calculation

jthi — Wed, 21 May 2025 11:36:10 GMT

I'm pretty sure that is calculated from your data. Expected Out of Spec rate uses different calculation and makes some assumptions on your data.

Re: “Out of spec rate” calculation

MFellermann — Wed, 21 May 2025 14:02:24 GMT

Thanks again Jarmo.
This is quite helpful. Do you know, where I can find the formula how the “Expected Out of Spec rate” is calculated?

Thank you in advance.

BR,

Maximlian

Re: “Out of spec rate” calculation

jthi — Wed, 21 May 2025 15:24:30 GMT

Most likely the normal calculations when you wish to calculate the probability that a normally distributed value is greater/less than (or both) than a specific value when you have known normal distribution.