I think what Elo's friends mean is that the constants hard-coded into Nelson's rules reflect some assumption on sample size. With a big sample, you'll violate them all the time and it won't mean anything. But they are a good starting point for tuning the thresholds.
I think what Elo's friends mean is that the constants hard-coded into Nelson's rules reflect some assumption on sample size. With a big sample, you'll violate them all the time and it won't mean anything. But they are a good starting point for tuning the thresholds.
If you have many parallel sensors, then yes, a flag that occurs 5% of the time due to noise will flag on at least one twentieth of your sensors. Elo's point, as I understood it, was that they have a long history--which is not relevant to the applicability of SPC.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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