[R] What are Type II or III contrast? (contrast() in contrast package)

[Emmanuel Charpentier]

Le mercredi 03 février 2010 à 00:01 -0500, David Winsemius a écrit :
> On Feb 2, 2010, at 11:38 PM, Peng Yu wrote:
> 
> > ?contrast in the contrast package gives me the following description.
> > However, I have no idea what Type II and III contrasts are. Could
> > somebody explain it to me? And what does 'type' mean here?
> >
> >    *‘type’*: set ‘type="average"’ to average the individual contrasts
> >    (e.g., to obtain a Type II or III contrast)
> 
> In no particular order:
> http://courses.washington.edu/b570/handouts/type3ss.pdf
> http://core.ecu.edu/psyc/wuenschk/SAS/SS1234.doc
> http://n4.nabble.com/a-kinder-view-of-Type-III-SS-td847282.html
> 
> Don't expect any follow-up questions to be answered or further  
> citations offered. This is really more in the realm of statistics  
> education than an R specific question.

Nonwhistanding David Winsemius' closing remark, I'd like to add
something that should be requested reading (and maybe hinted at in
lm()'s help page) :

http://www.stats.ox.ac.uk/pub/MASS3/Exegeses.pdf

(BTW, despite is age, MASS *is* requested reading, and Bill Venables'
exegeses should be part of it).

HTH,

--
Emmanuel Charpentier, DDS, MsC :-)