3% is a black mark? On a sample size of "more than 20"? If they said "more than 20" I'm guessing the sample isn't much more than 20. It would be a stupid thing to say with a sample size of 100 or 1000. So 0/20 is 0% and 1/20 is 5% so 1 problem creates a black mark.
Here's a better statistic: CR = Zero credibility with a 99% confidence interval