“With data from an epidemic there is no question of whether a change has occurred. Change is everywhere. The question is whether we are getting better or worse. So while the process behavior chart may be the Swiss army knife of statistical techniques, there are times when we need to leave the knife in our pocket, plot the data, and then listen to them as they tell their story.”
—Dr. Donald J. Wheeler

I agree with Dr. Wheeler’s comment about process control charts. Yet, I’m seeing far too many of them being inappropriately used as naïve attempts to interpret the mountains of questionable Covid-19 data being produced. I’ve done a few charts myself out of curiosity but none that I feel are worth sharing. Dr. Wheeler’s two recent, excellent Quality Digest articles have been the sanest things written—with nary a control chart in sight.

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