[S] lo() within gam() vs. loess()

Steven Paul Millard (probstat@nwrain.com)
Thu, 26 Feb 1998 10:08:49 -0800


Hello,

Can someone explain to me why the following fits of lo() called within
gam() vs. loess() are not the same?

Also, is there a theoretical reason why you can't tell lo() to assume
family="symmetric" instead of family="gaussian"?

Thank you for your time!!

> dum.x <- seq(0, 2*pi, len=100)
> set.seed(10)
> dum.y <- sin(dum.x) + rnorm(100)
> plot(dum.x, dum.y)
> fit.gam <- gam(dum.y ~ lo(dum.x, span=0.5, degree=1))
> fit.loess <- loess(dum.y ~ dum.x, span=0.5, degree=1)
> summary(fit.gam$fitted - fit.loess$fitted)
Min. 1st Qu. Median Mean 3rd Qu. Max.
-0.0482 -0.01954 0.009125 0.009125 0.03779 0.06646

Sincerely,

--Steve M.

_____________
| *** | Steven P. Millard, Ph.D.
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