See @StatDave 's reply.  You can make it binomial like I offered, but with only 31 obs, neither of the count/discrete distributions mentioned will converge in distribution to a binomial distribution, so I wouldn't go that way.   SteveDenham ... View more

Just be sure to use dist=binary and do not multiply by 100, as you need the variable to be in the closed interval [0,1].   SteveDenham ... View more

It helps to have some experience with regulators on this.  Linear extrapolation of stability data has been done for years.  While that may not make it "right", there is an impressive track record.  The problem with shifting to any of the time series methods is that the number of time points on these studies is often too small to be able to estimate the parameters, the time points are not equally spaced, and the measurements are not on the same sample (i.e., several samples are taken at the initiation of the stability testing period, and then destructively analyzed at pre-determined time points).  Consequently, a lot of time series methods aren't robust enough to deal with this.   As far as survival analysis, I think you would need multiple samples to analyze at each pre-determined time point to be able to estimate the hazard ratio (failure rate).  Unless the synthesis has been scaled up to a near production level, there may not be sufficient test article to carry out a decent survival analysis.   So for once, I can understand the use of a not-quite-right method.   SteveDenham ... View more

@WillTheKiwi  Could you help me out here?  I need a good definition of compatibility limits, especially as compared to confidence limits and tolerance limits.  Without that, I have some hesitancy about assuming symmetric bounds on the variance components, as I would expect some kind of scaled chi-squared distribution rather than a t distribution.   SteveDenham ... View more