What sample size is needed in my Performance Qualification (PQ)?

The choice of sample size starts in Risk Management. You need to determine what defect rates are allowed based on classifying the defect types. More critical defects that cause serious harm to the user require better quality. Acceptable rates may vary from 0.1% for very serious defects up to 6-10% for cosmetic issues. You also must choose a confidence level for your final conclusions. 90% or 95% are common values. Once those two values are determined, calculating a sample size is just a math problem. Remember, you will have to justify the acceptable defect rate to outside auditors.



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