I am inspecting cracks on a product. lets say, I have not done a IMV for this inspection and sold over 350k products, and found that we have 3 complaints due to the cracks. how do I support the statement, we are doing better in terms of Conf/reliability even if we were to validate the inspections.What are you inspecting and what are you trying to accomplish? I can give you a basic run down, but it would help if you gave more info on what you're trying to do. Both sampling plans below have a confidence level of 95%
You can either use one of the standard sampling plans such as ANSI Z1.4 or Squeglia c=0. Most companies are moving towards Squeglia's c=0 sampling plans because it technically gives you the same result of the Z1.4 plans with less samples taken for measurement.
In your example, under Z1.4, under general inspection level 2 and an AQL of 1.0, your sampling code would be P and the number of samples you take would be 800. You could accept up to 14 defects within that 800 and only reject lot once you hit 15 defects. For c=0, you would take 90 samples and reject the lot on the first defect.
for validation AQL=.25% RQL=5%You must state a RQL and/or AQL level in order to establish a c number.
BUT can you clarify your situation: you state “lot size of 350k(all of them). Do you mean you will inspect all 350k parts? Or are you going to sample randomly from a lot of 350k.
by the way, lot size is actually irrelevant despite some plans that index n based on sample size.
Are you looking for the formulas to use?
Could you help me with formula, on how to proceed to furtherYou don’t need a sampling plan - you need to calculate the confidence interval about the defect rate.