We have tested 1300 devices and have had one failure. We have an additional 850 units to test, and we would like to know what level of confidence we have that there will be 1 or fewer failures in these next 850 devices.
Using the Binomial distribution equation, I have entered the defect proportion to (1/1300) = .000769 (using the historical data). My number of future samples is 850 and my allowable defects is 1 or fewer. The calculated probability of 1 or fewer failures is 0.86018.
On one of the Binomial calculators I found online, they say that the Confidence Level is 1-P, so in my case it would be 1-0.86018=13.982%. This seems awfully low to me. Is this the correct way to calculate the confidence level or am I doing something wrong here?