smoothing binary data

You could also try the gam function in package mgcv (latest version
0.3-2). The following uses a penalized regression spline and chooses the
degrees of freedom by GCV:

library(MASS)
data(birthwt)
attach(birthwt)
library(mgcv)
gam(low~s(age),family=binomial())

Family: binomial 
Link function: logit 

Formula:
low ~ s(age)

Estimated degrees of freedom:
 4.236948 

Alternatively, if you want more control over the degrees of freedom then
you could use an un-penalized regression spline (although these don't
give such "nice" smooths):

b<-gam(low~s(age,4|f),family=binomial()) # 4 knot regression spline 
plot(b)

Simon

  ______________________________________________________________________

Simon Wood  snw at st-and.ac.uk  http://www.ruwpa.st-and.ac.uk/simon.html
The Mathematical Institute, North Haugh, St. Andrews, Fife KY16 9SS UK
Direct telephone: (0)1334 463799          Indirect fax: (0)1334 463748 

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