I wrote a small tutorial software to demonstrate to my tecs the power of
EWMA QC charts as compared to the conventional Shewhart chart. The
exponentially weighted moving average control chart is a good alternative
when we are interested in detecting small shifts. This chart was introduced
in clinical chemistry QC by Neubauer (Clin Chem 1997; 43:594-601) but never
put into practice. I just uploaded an English version of the tutorial
programme on my web site. If you are interested, you may download it freely
at http://www.multiqc.com/ewma.htm and play around in the programme to:
1 Change the control limits.
2 Create a bias.
3 Increase the SD to simulate a decrease of precision.
4 Change the speed of the animation.
5 And see how many out-of-control points appear on the charts or read the
average run length
The tutorial is particularly suited for teaching QC through a video
projector. I intend to translate soon another tutorial on multivariate QC.
Philippe Marquis, MD
Service de biochimie-immunologie
Centre hospitalier régional
Metz - France
www.marquis-soft.com
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