# Calculating Sigma from standard deviation

Six Sigma – iSixSigma Forums Old Forums General Calculating Sigma from standard deviation

Viewing 7 posts - 1 through 7 (of 7 total)
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• #49831

ROSS
Member

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

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#171035

Outlier, MDSB
Participant

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 Belt

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#171036

George4
Participant

What does it mean:Master Dark Salmon Belt?
Thanks

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#171037

ROSS
Member

I 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?

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#171049

Tim
Member

4 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”).

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#171054

Outlier, MDSB
Participant

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=(x-xbar)/std. dev.
Outlier

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#171060

Dr. Ravi Pandey
Participant

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.

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