We have a production process with very low (ppm-ish) fail rates that we would like to monitor for fails. Rather than monitoring ppm fail rates, it is a stronger test to monitor the number of fails (or time) between them, under the assumption that they follow a binomial distribution. In an M chart (this is what we call it) you then calculate a Z score every time there is a fail and chart as usual. It's not clear that JMP has this capability, but maybe it exists under a different name. Can anyone comment? We are using JMP 15.2 Pro.
Click the Shewhart Variables button in the control panel on the left side of Control Chart Builder and select Rare Event. You can make a G-chart (negative binomial distribution model) or a T-chart (Weibull distribution model).
Thanks Mark. Unfortunately that doesn't seem to quite be what I need. I can pre-process my data to convert from PPFPPPPPFPPF, etc. into counts of # of passes between each fail, and that has a negative binomial distribution. The strategy you recommend seems to calculate limits based on the percentile points of the observed distributions. However for a control chart I need to put in control limits based on a maximum allowed success (=Fail) probability (e.g., 1 ppm), rather than what is observed in the sample. Our general methodology is to map the binomial percentile to a z score using the inverse normal CDF, so that a value of -3 is a good lower limit; using that approach my data set averages around z = -4.7. The lower limit on the JMP chart is 0 however, which is essentially z = -INF. Do you have any recommendations?
You can right-click on the chart and select Limits > Set Control Limits. You can now enter your pre-determined limits this way.