Imagine you launched an ad campaign and got 5 conversions from 1000 clicks. Let's say you launch a second ad campaign and also get 1000 clicks.

What is the probability that you will also get 5 conversions? To take this variability into account, statistics use a confidence level and a confidence interval.

The trust level is the probability that the actual CR value is within a certain interval. The higher the confidence interval value, the more likely the site is to be blacklisted, even in the absence of data; the lower the value, the less likely the site is to be blacklisted, the recommended value is 90%.