Nelson Rules
Out of curiosity, with a regular normal distribution I wonder what the probability is that the most recent point finds a problem. I guess you could calculate these things separately for an approximation, but I'd probably just want to simulate it...For a first cut:- Rule 1: 0.3% of samples are more than 3 standard deviations of the mean.- Rule 2: 1/2^8 = 0.4% chance the previous 8 points were on the same side of the mean as the most recent one.- Rule 5: 2.5% chance of being above 2sd on either side, 3 choose 2 is 3, 2 sides, so 0.375% of exactly 2. "2 or 3" is not much higher.- Rule 6: More than 0.55%, if I've done my maths right.- Rule 7: 0.3%I guess you're going to get a lot of false positives if you're sampling reasonably frequently -- maybe one in 50?