I am new to using the Stability Analysis function (under Reliability and Survival –> Degradation –> Stability Test) in JMP (ver. 14), and I have some general questions about this tool. Apologies in advance for the rather wide-open “please help” questions.
Q1: Is this function appropriate to use for on-going monitoring of stability lots, where different lots will be at different timepoints? Or do all timepoints have to be completed before analysis?
Q2: Confidence Intervals. In Minitab Stability Module, the Confidence Interval used would usually be an Upper or Lower One-Sided CI, depending on whether the spec was an Upper or Lower Limit. But in my three examples (attached), the CI always seems to be Lower One-Sided (look in Prediction Settings in the red triangle next to Degradation Data Analysis), no matter the limit or what direction the data is trending. And yet the Overlay Charts seem to be showing 2-Sided (I think – it’s hard to see). It also looks like the Inverse Prediction graphs are showing one-sided confidence intervals, and the Prediction Graph tabs are showing 2-sided. Why aren’t these all the same? [you will have to enter 24 months and select confidence interval from the drop down to see the prediction graph]. How can I tell what is being used for the Stability Test section?
Q3: How do I interpret the Inverse Prediction tab in my Test 2 example? Why are some lines going all the way to zero, but the predicted shelf life is approximately 24 months?
Q4: Also in the Test 2 example, the Prediction Graph shows Lot M confidence interval going beyond the specification at 24 months, but the Stability Tests section indicates the expiration is 24.3282. Why don’t these align?
Q5: Does it make sense to do a shelf life prediction for Test 2? It seems like it is mostly variability and not actual change over time. Is there an objective way to evaluate if a shelf life projection should be done?
My Examples (attached):
Test 1: Upper Spec Limit = 2.9. Increasing Slope. Shelf Life = 24 months.
Test 2: Upper Spec Limit = 14.6. Not much of a Slope in either direction. Shelf Life = 24 months.
Test 3: : Lower Spec Limit = 78.5, Decreasing Slope. Shelf Life = 24 months.
Thank you!