Re: [S] Fw: difference between predict

alain Le Tertre (alain@worldnet.fr)
Wed, 26 Aug 1998 09:21:01 +0200


Thanks for your response.
I misunderstood that constant (intercept) was not the coefficient of the
intercept, but the constant attribute.

-----Original Message-----
From: Prof Brian D Ripley <ripley@stats.ox.ac.uk>
To: alain Le Tertre <alain@worldnet.fr>
Cc: s-news <s-news@wubios.wustl.edu>
Date: mardi 25 août 1998 13:24
Subject: Re: [S] Fw: difference between predict

>On Tue, 25 Aug 1998, Prof Brian D Ripley wrote:
>
>> On Tue, 25 Aug 1998, alain Le Tertre wrote:
>>
>> > I have received some e-mail from people who need the answer, but no
answer,
>> > even from s-help.
>> > So, i'll resend my question.
>> > -----Original Message-----
>> > From: alain Le Tertre <alain@worldnet.fr>
>> > To: s-news <s-news@wubios.wustl.edu>
>> > Date: mercredi 29 juillet 1998 10:24
>> > Subject: difference between predict
>> >
>> >
>> > >In S-plus 4 guide to statistics p 221, "Specifying type="terms" allows
you
>> > >to compute the component of the prediction for each term separately.
>> > Summing
>> > >the columns of the matrix and adding the constant (intercept) term is
>> > >equivalent to specifying type="link"".
>> > >So try :
>> > >zzz_gam(Kyphosis ~ poly(Age, 2) + s(Start), data = kyphosis)
>> >
>cbind(predict(zzz,type="link"),zzz$coef[1]+rowSums(predict(zzz,type="terms"
>> > )
>> > >))
>> > >give you :
>> > >1 1.6582944 2.059893
>> > > 2 1.1161389 1.517737
>> > > 3 1.6671144 2.068713
>> > > 4 1.1938420 1.595441
>> > > 5 0.8517588 1.253357
>> > > 6 0.8213737 1.222972
>> > > 7 1.0687632 1.470362
>> > > 8 1.0036325 1.405231
>> > > 9 1.1289169 1.530515
>> > >10 1.2703754 1.671974
>> > >11 1.1993687 1.600967
>> > >[snip]
>> > >Did i misunderstand something?
>>
>> Yes, you forgot what you did. That is not the answer I get in any version
>> of S-PLUS, including 4.0. For predict(zzz,type="terms") I get
>
>Clarification: I misread your code, but my reasoning is correct. (Why are
>you so adverse to spaces? It makes S code so much harder for humans to
>parse.) The constant mentioned is not zzz$coef[1], nor is the
>`(Intercept)', it is the constant attribute.
>
>--
>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 272860 (secr)
>Oxford OX1 3TG, UK Fax: +44 1865 272595
>
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