Six Sigma – iSixSigma Forums Old Forums General Quadric Regression Equation

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• #49768

David Hogan
Participant

Hello all,
I have a quadratic expression equation from minitab:
Y = 0.02129 + 0.000606 Interval – 0.000001 Interval**2
Question:  what is the **2?  Is that telling me to square my Interval value?
David

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#170530

clb1
Participant

Yes.

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#170546

BTDT
Participant

David:Yes, the “0.000001 Interval**2” term means square the value of Interval and multiple by 0.000001.If this is from a DOE run or response sruface run then make sure you use the correct equation.

If you have numerical values for your high and low settings, Minitab will give you an equation where you use the numerical values of the settings, (eg, 2.1, 3.5, 4.9 – called “uncoded”) and a second equation where you use the standard settings, (eg. -1, 0, +1 – called “coded”). This is an option use can change when running the analysis.If there is any doubt, select “storage” and select “fits” and let the program input your Xs and make the prediction for each observation. You can do a few hand calculations to check the numbers.Cheers, Alastair

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#170568

BC
Participant

David,
Maybe you aren’t familiar with Fortran.  Double asterisks are the exponentiation symbol.  So yes, A**2 means “A squared”.
Maybe Minitab should replace “**” with the more familiar “^”.

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