Re: Sample size for Design Verification / Design Validation
My comment concerns design verification ONLY.
What I see is that for design verification, one has, at least in our case, a limited number of "near production" devices
I'm in same situation. I have recently inherited QA role and I'm trying to stumble my way through the statistics and sample size.
Our current procedures utilizes combination of Bayes Success Run chart, AQL chart, and LTPD charts. I've been reading Juran's handbook, Guide to Acceptance by Wayne Taylor, along with whatever I can find online. It seems most of these plans make an assumption that lot size is 10x sample size and seems to apply mostly to processes and ongoing manufacturing. Couple of our projects have limited # of units, and sample sizes from these type of charts are not achievable.
Some plans also mention STI (statistical tolerance intervals) within spec? I believe this allows for fewer samples to used with distribution software (Distribution Analyzer or StatGraphics) to show small sample is within specified confidence/reliability interval without justification for # samples used.
For example, Our design verification plans simply increase confidence/reliability requirements with increasing risk..
risk 1 - 90/95
risk 2 - 95/97
risk 3 - 95/99
for 95 confidence/95 reliability w/ variable data
-LTPD (5% defective) chart shows n=20, Ppk=0.81, Pp=0.87..
- software requires min 8 samples to perform calculations
Looks like Bev D mentioned this over here
"Qualification and Validation (including 21 CFR Part 11)" (can't post link)
Not sure this is valid or how to justify..
Or how to reduce sample size for attribute data.
95/97 on Bayes-Success , n = 98
somehow make it a variable type of data or 100% inspection of a much smaller sample??
I seen some sample size calculations for FDA Verification and Validation posted by Bev D, "Determining Sample Size for FDA Verification and Validation Activities", but we do not have a delta, new product, no historical data to compare
Are there any charts or sampling plans that focus on design validation/verification rather than process and mfg?
Thanks