Confidence intervals and polynomial fits
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 http://biology.mcgill.ca/grad/ben/
David Winsemius, MD West Hartford, CT