Clarifying my question:
options(contrasts = c("contr.sum", "contr.poly"))
> contrasts(fixw$snconv)
[,1] [,2] [,3] [,4] [,5]
01 1 0 0 0 0
03 0 1 0 0 0
05 0 0 1 0 0
06 0 0 0 1 0
07 0 0 0 0 1
09 -1 -1 -1 -1 -1
I need to force the coefficient on level 03 to be zero.
Thank you.
Stephen Bond
-----Original Message-----
From: David Winsemius [mailto:dwinsem...@comcast.net]
Sent: Wednesday, July 07, 2010 3:44 PM
To: Bond, Stephen
Cc: r-help@r-project.org
Subject: Re: [R] forcing a zero level in contr.sum
On Jul 7, 2010, at 3:13 PM, Bond, Stephen wrote:
> I need to use contr.sum and observe that some levels are not
> statistically different from the overall mean of zero.
> What is the proper way of forcing the zero estimate? It seems the
> column corresponding to that level should become a column of zeros.
> Is there a way to achieve that without me constructing the design
> matrix?
> Thank you.
lm( formula = z ~ x + y + 0, ...) _might_ do something close to
what you want.
David Winsemius, MD
West Hartford, CT
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