“Out of spec rate” calculation

[#1]

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

[#2]

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.

[#3]

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

Thank you in advance.

[#4]

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.

[#5]

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

[#6 · Accepted solution]

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.