Seven sun rule help
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 This topic has 6 replies, 6 voices, and was last updated 12 years, 1 month ago by SPC rulez.

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December 16, 2009 at 4:46 am #53037
TierradentroParticipant@john Include @john in your post and this person will
be notified via email.This is a question question about why seven is used in the seven run rule for seven continuous controls points below or above the mean. I have researched a lot of QA databases and I haven’t been able to get an answer to this question. Any assistance will be greatly appreciated.
0December 16, 2009 at 8:05 am #187561Perhaps it has something to do with the likelihood of that event
0December 17, 2009 at 8:47 am #187601
SchafheutleParticipant@Markus Include @Markus in your post and this person will
be notified via email.Hi John
the reason is very straitforward: How big is the probability that the next point in a data series is below or above the previous one? 0.5. How big is it that 3 in a row are all above or below the all previous? 0.5 x 0.5 = 0.25. So having 7 in a row all above or below the previous makes 0.5×0.5×0.5×0.5×0.5×0.5=0.015. Five in a row have the probability of 0,063. Depending on the risk of drawing wrong conclusions you would prefer 5 or 7 in a row. The risk will vary between 1.5 to 6.3%. Or otherwise said the probability of being right is 94.7 to 98.5%.
Are you familiar with these numbers? They are in the standard range of 2 to 3 sigma which is the control charting agreement of having noise or special causes. So having 5 to 7 datapoint steadily increasing or decreasing point with high probability to a special cause effect.
Regards Markus0December 17, 2009 at 4:14 pm #187616EXCELLENT EXPLAINATION !!
0December 18, 2009 at 1:16 am #187622
Owen ChangParticipant@OwenChang Include @OwenChang in your post and this person will
be notified via email.Thanks a lot! It really a good lesson learned for me.
Happy New Year!0December 18, 2009 at 12:23 pm #187632
SPC rulezMember@SPCrulez Include @SPCrulez in your post and this person will
be notified via email.Masterbook of SPC, answers for all questions (original language of course ;))
http://www.teknologiainfo.net/default.asp?docId=12360&productId=143670December 18, 2009 at 12:31 pm #187633
SPC rulezMember@SPCrulez Include @SPCrulez in your post and this person will
be notified via email.Broken link, another try:
http://www.teknologiainfo.net/default.asp?docId=12360&productId=14367&fromSearch=true
Or by google: “Suorituskykyiset prosessit, hyödynnä SPC”0 
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