iSixSigma

Seven sun rule help

Six Sigma – iSixSigma Forums Old Forums General Seven sun rule help

Viewing 7 posts - 1 through 7 (of 7 total)
  • Author
    Posts
  • #53037

    Tierradentro
    Participant

    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.

    0
    #187561

    Mikel
    Member

    Perhaps it has something to do with the likelihood of that event

    0
    #187601

    Schafheutle
    Participant

    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 Markus

    0
    #187616

    anupam
    Participant

    EXCELLENT EXPLAINATION !!

    0
    #187622

    Owen Chang
    Participant

    Thanks a lot! It really a good lesson learned for me.
    Happy New Year!

    0
    #187632

    SPC rulez
    Member

    Masterbook of SPC, answers for all questions (original language of course ;-)) 
    http://www.teknologiainfo.net/default.asp?docId=12360&productId=14367

    0
    #187633

    SPC rulez
    Member

    Broken link, another try:
    http://www.teknologiainfo.net/default.asp?docId=12360&productId=14367&fromSearch=true
    Or by google: “Suorituskykyiset prosessit, hyödynnä SPC”

    0
Viewing 7 posts - 1 through 7 (of 7 total)

The forum ‘General’ is closed to new topics and replies.