Ideas from the Tiger’s Head by Simon Caulkin, The Observer. This is a remarkably nuanced short article on control charts given that it is a newspaper article (which normally overly simplify such concepts to the point not much of value is left).
This is a critical distinction: if managers mistakenly tamper with a stable process, believing an occurrence is exceptional, they introduce an external cause, which destabilises it. Targets do the same thing.
If a system is stable, as a matter of logic you can only force it to deliver a target beyond its limits by improving it, distorting it or fiddling the numbers.
Previous post relating to the last sentence: Dangers of Forgetting the Proxy Nature of Data
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The best quality control tool I’ve ever seen is control chart. Within two lines along a straight line ( mean production) you can see how accurately you are on the target. The best thing about CC is that
it actually dignosis the errors before they happen hence the process remains very much under
control.