I have a lot of 1,000 parts. We ran a test on a sample size of 50. We had 12 failures.
A colleague did the following calculation in excel:
Using a 80% confidence level....
=BETAINV(1-.8,38,12+1)
The result was 0.6653 and therefore, the conclusion was the we could be 80% confident that at least 66.5% of the lot were good parts.
Is that the correct way to approach this issue? Is the formula correct? And is that a proper conclusion from that formula?
