> To: Kenneth Cabrera <krcabrer at epm.net.co>
> From: Peter Dalgaard BSA <p.dalgaard at biostat.ku.dk>
> Date: 12 Apr 2000 11:23:09 +0200
>
> Kenneth Cabrera <krcabrer at epm.net.co> writes:
>
> > Hi, everybody!!
> >
> > How can I calculate the Type III ss, as defined by SAS, for a linear
regresion?>
> Like this:
>
> > drop1(lm1, test="F")
> Single term deletions
My belief is that does not work with models with interactions, which is
where the Type III notation comes into its own (mess).
> options(contrasts=c("contr.helmert", "contr.poly"))
> example(warpbreaks)
> drop1(fm1)
Single term deletions
Model:
breaks ~ wool + tension + wool:tension
Df Sum of Sq RSS AIC
<none> 5745.1 264.0
wool:tension 2 1002.8 6747.9 268.7
> drop1(fm1, . ~ .) # as suggested by Bill Venables
Single term deletions
Model:
breaks ~ wool + tension + wool:tension
Df Sum of Sq RSS AIC
<none> 5745.1 264.0
wool 1 450.7 6195.8 266.1
tension 2 2034.3 7779.4 276.4
wool:tension 2 1002.8 6747.9 268.7
looks as if it does work in R (we know it works in S-PLUS, as Bill found
out when trying to do the opposite). However, watch out as
> drop1.default(fm1, . ~ .)
Single term deletions
Model:
breaks ~ wool + tension + wool:tension
Df AIC
<none> 264.02
wool 0 264.02
tension 0 264.02
wool:tension 2 268.71
does respect the hierarchy, and is probably what drop1.lm should have
given. (Looks like I did copy one of the S errors, probably deliberately, when
I wrote drop1.*.)
--
Brian D. Ripley, ripley at 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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