logistic regression lrm() output
Why is a one unit change in x an interesting range for the purpose of estimating an odds ratio? The default in summary() is the inter-quartile-range odds ratio as clearly stated in the rms documentation. Frank
array chip wrote:
Hi, I am trying to run a simple logistic regression using lrm() to calculate a odds ratio. I found a confusing output when I use summary() on the fit object which gave some OR that is totally different from simply taking exp(coefficient), see below:
dat<-read.table("dat.txt",sep='\t',header=T,row.names=NULL)
d<-datadist(dat) options(datadist='d') library(rms) (fit<-lrm(response~x,data=dat,x=T,y=T))
Logistic Regression Model
lrm(formula = response ~ x, data = dat, x = T, y = T)
Model Likelihood Discrimination Rank Discrim.
Ratio Test Indexes Indexes
Obs 150 LR chi2 17.11 R2 0.191 C 0.763
0 128 d.f. 1 g 1.209 Dxy 0.526
1 22 Pr(> chi2) <0.0001 gr 3.350 gamma 0.528
max |deriv| 1e-11 gp 0.129 tau-a 0.132
Brier 0.111
Coef S.E. Wald Z Pr(>|Z|)
Intercept -5.0059 0.9813 -5.10 <0.0001
x 0.5647 0.1525 3.70 0.0002
As you can see, the odds ratio for x is exp(0.5647)=1.75892.
But if I run the following using summary():
summary(fit)
Effects Response : response Factor Low High Diff. Effect S.E. Lower 0.95 Upper 0.95 x 3.9003 6.2314 2.3311 1.32 0.36 0.62 2.01 Odds Ratio 3.9003 6.2314 2.3311 3.73 NA 1.86 7.49 What are these output? none of the numbers is the odds ratio (1.75892) that I calculated by using exp(). Can any explain? Thanks John [[alternative HTML version deleted]]
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----- Frank Harrell Department of Biostatistics, Vanderbilt University -- View this message in context: http://r.789695.n4.nabble.com/logistic-regression-lrm-output-tp3533223p3533278.html Sent from the R help mailing list archive at Nabble.com.