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There’s nothing normal about SPC!

There’s nothing normal about SPC! Knocks the final few nails into the coffin which contains the remains of the notion that the theory and practice of control charting depend on assumptions of normality. The subject’s creator, Dr Walter Shewhart, denied this as long ago as 1939! His most famous student, Dr W. Edwards Deming, denied it repeatedly thereafter. There appear to be two most crucial arguments as to why the “orthodox” statistician claims that normality is necessary. One is to enable probability interpretations of control limits. The other is to justify the conversion factors which are in common use in control‐chart calculations. The truth is that, even under normality, the usual probability interpretations are meaningless in practice and that, in the latter case, the behaviour of the conventional conversion factors is not at all dependent on normality but is in fact very similar over a wide range of differently‐shaped probability distributions. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Training for Quality Emerald Publishing

There’s nothing normal about SPC!

Training for Quality , Volume 5 (3): 6 – Sep 1, 1997

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Publisher
Emerald Publishing
Copyright
Copyright © 1997 MCB UP Ltd. All rights reserved.
ISSN
0968-4875
DOI
10.1108/09684879710173352
Publisher site
See Article on Publisher Site

Abstract

Knocks the final few nails into the coffin which contains the remains of the notion that the theory and practice of control charting depend on assumptions of normality. The subject’s creator, Dr Walter Shewhart, denied this as long ago as 1939! His most famous student, Dr W. Edwards Deming, denied it repeatedly thereafter. There appear to be two most crucial arguments as to why the “orthodox” statistician claims that normality is necessary. One is to enable probability interpretations of control limits. The other is to justify the conversion factors which are in common use in control‐chart calculations. The truth is that, even under normality, the usual probability interpretations are meaningless in practice and that, in the latter case, the behaviour of the conventional conversion factors is not at all dependent on normality but is in fact very similar over a wide range of differently‐shaped probability distributions.

Journal

Training for QualityEmerald Publishing

Published: Sep 1, 1997

Keywords: Control charts; Probability; Statistical process control

References