Re: [R] Confidence intervals and polynomial fits

From: David Winsemius <>
Date: Fri, 06 May 2011 16:27:17 -0400

On May 6, 2011, at 4:16 PM, Ben Haller wrote:
> As for correlated coefficients: x, x^2, x^3 etc. would obviously be
> highly correlated, for values close to zero.

Not just for x close to zero:

 > cor( (10:20)^2, (10:20)^3 )
[1] 0.9961938
 > cor( (100:200)^2, (100:200)^3 )
[1] 0.9966219

> Is this what you mean, as a potential source of problems? Or if you
> mean that the various other terms in my model might be correlated
> with x, that is not the case; each independent variable is
> completely uncorrelated with the others (this data comes from
> simulations, so the independent variables for each data point were
> in fact chosen by random drawing).
> It didn't seem easy to post an example, since my dataset is so
> large, but if either of you would be willing to look at this
> further, I could upload my dataset to a web server somewhere and
> post a link to it. In any case, thanks very much for your help;
> I'll look into the things you mentioned.
> Ben Haller
> McGill University

David Winsemius, MD
West Hartford, CT mailing list PLEASE do read the posting guide and provide commented, minimal, self-contained, reproducible code. Received on Fri 06 May 2011 - 20:29:01 GMT

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