On Jul 7, 2010, at 4:04 PM, Bond, Stephen wrote:
Clarifying my question:
options(contrasts = c("contr.sum", "contr.poly"))
contrasts()
[,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.
?factor
?relevel
Perhaps worth a try:
fixw$snconv <- relevel(fixw$snconv, ref="03")
(But I wonder if using contr.sum will ever generally satisfy that
goal, since contr.sum calculates the difference from a grand mean and
this will only work if a) the GM=0 and b) there is only one term on
the RHS of the model, and c) probably a bunch of other restrictions.)
--
David.
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
David Winsemius, MD
West Hartford, CT
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