I got involved with Total Quality 20 years ago, did the Deming 3-day, but couldn't do that stuff now to save my life. One of the things control charts give you is "flags" for an out-of-control process. 7 consecutive points in one direction, or 7 in a row above or below the line, and you have to ask what's going on. Single events outside the lines tend to be "special cause" events -- if traffic deaths in Ohio are 'under control" with 25 to 30 per week, and suddenly there's a 65 week, your control chart will show that -- and investigation shows that a school bus went over a bridge. Not something you can predict or even have to do something about, even though it's a horrific example. "Common cause" variations are much harder to identify and correct. Those would be trolls, IMO.
Ha-ha. I remember being sent to a TQI class when I was aa two-striper airman. Was completely lost on me.
____
Unrelated was that was the day I found out one of my co workers drowned and two others had to be rescued because they went over a waterfall in a inflatable boat they had no business riding in.