Apr 24 2024
When Not to Connect the Dots
When plotting a sequence of points, should we connect the dots into a line? We usually do, but it shouldn’t be a foregone conclusion. Every chart element should have a clear and precise meaning: if we can’t explain what it means or it is ambiguous, it confuses readers and we should omit it.
The bulk of the SPC literature shows Control Charts as broken-line graphs. 100 years ago, Walter Shewhart, the inventor of these charts, plotted separate points instead. He did not explain why, so it’s on us to try and figure out what may have been his reasons.
Jun 15 2024
True And False Alarms in Quality Control
The SPC literature does not consider what happens when an organization successfully uses its tools. It stabilizes unstable processes so that disruption from assignable causes becomes increasingly rare. While this happens, the false alarms from the common causes remain at the same frequency, and the ratio of true to false alarms drops to a level that destroys the credibility of the alarms.
This is a signal that further quality improvement can only be pursued with other tools, typically the conversion to one-piece flow to accelerate the detection of problems and, once human error becomes the dominant cause of defects, error-proofing. This article digs into the details of how this happens with control charts.
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By Michel Baudin • Quality • 4 • Tags: Control Chart, False Alarm, Quality, SPC, True Alarm