So actually your number, by Laplace's law of succession (http://en.wikipedia.org/wiki/Rule_of_succession), would be 71%: you saw 4 other instances and you were another instance, so that's 5 instances, and you say you and 3 others were pulled over for 4 pull overs, so in the formula 's +1 / n + 2' we get ' 4+1 / 5+2' or 0.71 or 71%.