Very interesting discussion going on here. I have dealt with this issue for many years, I mean a lot of them. The fact of the matter is that it has become a crutch for many of those assigned the responsibility of investigating these CARs. It is, and should continue to be a step along the way of determining the root cause but not a stand alone, because it can always have a reason why there was operator error. I will tell you another crutch in this area and that is "Trend Analysis". This is given in many cases when the investigator doesn't feel there is enough data to make an immediate decision as to root cause. Well, how much is enough? Again, used way too much in situations like this.