On Jun 18, 2010, at 5:16 PM, David Winsemius wrote:
On Jun 18, 2010, at 5:13 PM, David Winsemius wrote:
On Jun 18, 2010, at 12:02 PM, Josh B wrote:
Hi all,
I am looking to fit a logistic regression using the lrm function
from the Design library. I am interested in this function because
I would like to obtain "pseudo-R2" values (see http://tolstoy.newcastle.edu.au/R/help/02b/1011.html)
.
Can anyone help me with the syntax?
If I fit the model using the stats library, the code looks like
this:
model <- glm(x$trait ~ x$PC1 + I((x$PC1)^2) + I((x$PC1)^3), family
= binomial)
What would be the equivalent syntax for the lrm function?
Not sure if the code you gave above produces an orthogonal set, but
perhaps this will be meaningful to some of r-help's readers (but
not necessarily to me):
require(Design)
mod.poly3 <- lrm( trait ~ poly(PC1, 3), data=x)
This does report results, but I'm not sure how you would interpret.
(See below for one attempt)
I think Harrell would probably recommend using restricted cubic
splines, however.
mod.rcs3 <- lrm( trait ~ rcs(PC1, 3), data=x)
For plotting with Design/Hmisc functions, you will get better
results with the datadist facilities.
> ddx <- datadist(x)
> options(datadist="ddx")
> plot(mod3, PC1=NA)
Forgot to fix this:
plot(mod.rcs3, PC1=NA)
# Perfectly sensible plot which includes the OR=0 line that would
be the theoretically ideal result.
That would be log(odds) = 0 or OR=1. I wonder how many other errors I
committed?
--
DW
# Whereas plot.Design does not know how to plot the earlier result
> plot(mod.poly3, PC1=NA)
Error in plot.Design(mod.poly3, PC1 = NA) :
matrix or interaction factor may not be displayed
May still get meaningful results with predict:
plot(seq(-3, 2, by=.1), predict(mod.poly3, data.frame(PC1=seq(-3,
2, by=.1)) ) )
Bit it appears to be less satisfactory that the rcs fit, since it
blows up at the extremes.
--
David.
Thanks very much in advance,
-----------------------------------
Josh Banta, Ph.D
Center for Genomics and Systems Biology
New York University
100 Washington Square East
New York, NY 10003
Tel: (212) 998-8465
http://plantevolutionaryecology.org
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David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT
David Winsemius, MD
West Hartford, CT
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
