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?