Re: [R] Prediction using GAM

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Thu 24 Mar 2005 - 19:00:48 EST

R has *two* gam() functions in contributed packages 'mgcv' and 'gam'. Which is this?

Please see the posting guide and provide a reproducible example.

If this is package 'gam', prediction difficulties of this sort for the S version are discussed in the White Book, MASS and elsewhere (but I recall reading that they did not apply to the R version).

On Wed, 23 Mar 2005, Kerry Bush wrote:

> Recently I was using GAM and couldn't help noticing
> the following incoherence in prediction:
>
>> data(gam.data)
>> data(gam.newdata)

It is unusual to use data() on your own objects, but we cannot reproduce what you did without data.

>> gam.object <- gam(y ~ s(x,6) + z, data=gam.data)
>> predict(gam.object)[1]
> 1
> 0.8017407
>>
> predict(gam.object,data.frame(x=gam.data$x[1],z=gam.data$z[1]))
> 1
> 0.1668452
>
> I would expect that using two types of predict
> arguments should give me the same results.
> When I used this to predict a new data set then it
> seems OK:
>
>>
> predict(gam.object,data.frame(x=gam.newdata$x[1],z=gam.newdata$z[1]))
> 1
> 0.4832136
>> predict(gam.object,gam.newdata)[1]
> 1
> 0.4832136
>
> Could anybody explain the strange behavior of
> predict.gam function?

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

______________________________________________
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Received on Thu Mar 24 19:05:20 2005

This archive was generated by hypermail 2.1.8 : Fri 03 Mar 2006 - 03:30:55 EST