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Community Trekker

## DOE Results

In the DOE results, why is it possible that the parameter estimate for factor X is positive and for X*X negative, or vice versa?

1 ACCEPTED SOLUTION

Accepted Solutions
Community Trekker

## Re: DOE Results

The parameter estimates are estimates of the constants (b's in my exaple below) of a second order polynomial fit to the data, e.g.

Y = b2 * X^2 + b1 * X + b0.

The coefficient you mention are b1 and b2 respectively, whereas b0 would be the intercept of your model. The b2 coefficient determines the shape of the fit, that is negative b2: "frowning face curve" and positive b2: "smiley face curve". The b1 coefficient (together with the intercept, b0) determines the location of the curve. So in short the parameter estimate for factor X  and X*X are two very different things describing different characteristics of the fitted curve.

BR
Jesper
3 REPLIES 3
Community Trekker

## Re: DOE Results

The parameter estimates are estimates of the constants (b's in my exaple below) of a second order polynomial fit to the data, e.g.

Y = b2 * X^2 + b1 * X + b0.

The coefficient you mention are b1 and b2 respectively, whereas b0 would be the intercept of your model. The b2 coefficient determines the shape of the fit, that is negative b2: "frowning face curve" and positive b2: "smiley face curve". The b1 coefficient (together with the intercept, b0) determines the location of the curve. So in short the parameter estimate for factor X  and X*X are two very different things describing different characteristics of the fitted curve.

BR
Jesper
Community Trekker