Recently my R&D engineers and I have been having a dispute about sample sizes. They have fallen in love with a book that they have used at a previous company, Wayne Taylor's Statistical Procedures for the Medical Device Industry. I have no problem with the book, but they've latched on to one component discussed in Appendix A of STAT-03, which is the "Stress Condition."
According to Dr. Wayne, the "Stress test is expected to produce more failures than will occur under normal conditions." He says the stress test rate must be 5x the nominal failure rate, and conveniently mentions Ship testing per ASTMs as an established stress condition. This allows for a reduced sample size, from the nominal 95/95 we would have (59 samples attribute) to 90/90 (22 samples) based on being able to create and detect failures at a higher rate.
I have personally never heard of reducing a sample size because you are using an established ship method that is "worst-case" but who am I to disagree with a statistician. I just can't get over all my experience at previous companies using at least 95/95 for product sterility.
Anyone have experience with this method? Does it fly with FDA/NBs?
According to Dr. Wayne, the "Stress test is expected to produce more failures than will occur under normal conditions." He says the stress test rate must be 5x the nominal failure rate, and conveniently mentions Ship testing per ASTMs as an established stress condition. This allows for a reduced sample size, from the nominal 95/95 we would have (59 samples attribute) to 90/90 (22 samples) based on being able to create and detect failures at a higher rate.
I have personally never heard of reducing a sample size because you are using an established ship method that is "worst-case" but who am I to disagree with a statistician. I just can't get over all my experience at previous companies using at least 95/95 for product sterility.
Anyone have experience with this method? Does it fly with FDA/NBs?