Whiteboard: Control Charts 1

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[@TheEngineeringToolboxChannel]

Up-vote and sub for correctly pointing out the difference between sigma hat and global SD. So many videos out there get this wrong and because of it we have so many people out there creating control charts that literally tell them nothing about their process.

[@joshuaerkman1444]

Sd *3 = SL for almost all process control.

[@cmdctrl]

SD assumes homogeneity in the data. In a control chart you are looking to if there is any. This the successive differences method of Shewhart is used not Sd. See The Don Wheeler’s paper here. www.qualitydigest.com/inside/six-sigma-column/right-and-wrong-ways-computing-limits-010710.html

[@TheEngineeringToolboxChannel]

Incorrect. Sigma-hat is a very different thing than SD (global standard deviation). Sigma-hat is an estimated short term variation where SD is a measure of overall variation.

[@TheEngineeringToolboxChannel]

C Dagnan I’m glad to see other people who realize the difference. This is one of the few videos that correctly points out the difference between global standard deviation and estimated short term standard deviation.