# 1.5 sigma shift – is it plus/minus or overall?

Six Sigma – iSixSigma Forums Old Forums General 1.5 sigma shift – is it plus/minus or overall?

Viewing 6 posts - 1 through 6 (of 6 total)
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• #32973

jediblackbelt
Participant

A real quick question on a subject that is beaten to death.  Does the shift work as a +/- 1.5 sigma or is the overall spread for a +/-.75 sigma?

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#88614

Ron
Member

+/-  1.5

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#88619

melvin
Participant

From our experience we understand that the 1.5 Sigma shift is one sided.  Hope this helps…

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#88620

rwatters
Member

Eg. If your short term capability equals 3.2, your longterm would then equal 1.7.
Add the 1.5 if youre going from long term to short term

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#88622

mcleod
Member

Bob is correct. The addition or subtraction of 1.5 is a one-sided calculation.
If you use minimum capability analysis to determine Z or sigma level, you would EITHER add or subtract 1.5 to this number (depending on whether you are converting to short-term or long-term).
The most customary approach is to determine overall Z or sigma level by backing into it based upon total DPPM, then performing the addition or subtraction of 1.5 (again depending on whether you are converting to short-term or long-term).
However, despite what Mikel H. says, this conversion is nonsense! There is NO theoretical basis for such a conversion, and only very LIMITED empirical reasons for doing so.
Hope this helps.

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#88625

Mikel
Member

amen on the nonsense

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