Calculating Sigma from standard deviation
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 This topic has 6 replies, 5 voices, and was last updated 14 years, 7 months ago by Dr. Ravi Pandey.

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April 11, 2008 at 2:38 pm #49831
Can anyone tell me how to calculate the sigma value from a listed standard deviation. I have a datbase that helps me to caculate the standard deviatin and i would like to include the sigma value in this database. Thanks
0April 11, 2008 at 3:28 pm #171035
Outlier, MDSBParticipant@Outlier,MDSB Include @Outlier,MDSB in your post and this person will
be notified via email.Tony,
Your missing element is a customer specification limit. A Sigma level is the number of standard deviations between the mean and the nearest spec limit.
Outlier, Master Dark Salmon Belt0April 11, 2008 at 3:35 pm #171036
George4Participant@George4 Include @George4 in your post and this person will
be notified via email.What does it mean:Master Dark Salmon Belt?
Thanks0April 11, 2008 at 3:35 pm #171037I have the customer specs already in my database. I just need a matmatical equation that I can use to determine the sigma value using the specs as well as the deviation value. Any idea?
0April 11, 2008 at 5:47 pm #1710494 George – for insight to Master Dark Salmon Belt, visit http://www.ississippi.org (pronounced “i s s i s s i p p i dot org”).
0April 11, 2008 at 6:59 pm #171054
Outlier, MDSBParticipant@Outlier,MDSB Include @Outlier,MDSB in your post and this person will
be notified via email.Tony,
The formula is pretty easy:
The sigma level is the point of interest (or spec limit) minus the mean divided by the standard deviation.
z=(xxbar)/std. dev.
Outlier0April 11, 2008 at 11:47 pm #171060
Dr. Ravi PandeyParticipant@Dr.RaviPandey Include @Dr.RaviPandey in your post and this person will
be notified via email.Tony,
It is not going to be easy…unless you write a macro. If you follow the way people do it, you have to use the information standard dev and specs to understand rejects from both tails….then you need to add this. The added area now you have to put on the right side of the distribution and find the distance of the left edge of this area from mean.
It is so simple, and yet too complext. Now having said that, I have an article published by iSixSigma this Monday (it is a bit of read!). It addresses some issues but overall still it does not reduce work for you. If your defects are evenly split at both side of the specs, the method OUTLIER is saying should work and is easy and it is same as what the article talks about in this specific sit.0 
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