On Jun 20, 2012, at 21:05 , David Winsemius wrote: > > On Jun 20, 2012, at 12:12 PM, Sebastian Pölsterl wrote: > >> Hi, >> >> I'm using the rms package to do regression analysis using the lrm >> function. Retrieving odds ratios is possible using summary.rms. However, >> I could not find any information on how exactly the odds ratios for >> continuous variables are calculated. It doesn't appear to be the odds >> ratio at 1 unit increase, because the output of summary.rms did not >> match the coefficient's value. >> >> E.g. print gives me: >> >> Coef S.E. Wald Z Pr(>|Z|) >> age 0.1166 0.0289 4.04 <0.0001 >> >> whereas summary gives me: >> >> Factor Low High Diff. Effect S.E. Lower 0.95 Upper 0.95 >> age 27.0000 37.00000 10.0000 0.78 0.20 0.40 1.17 >> Odds Ratio 27.0000 37.00000 10.0000 2.19 NA 1.49 3.22 >> >> Does anybody know how these values are obtained, especially in the >> presence of interactions? > > It is explained in the first paragraph of ?summary.rms, : > > " By default, inter-quartile range effects (odds ratios, hazards ratios, > etc.) are printed for continuous factors," > > ... and the labeling makes it fairly clear (at least it was for me) that it > is an odds ratio for a change in predictor value from the 25th to the 75th > percentile (which are the values in the Low and High columns)
Begparding? Seems to me that would require (37-27)*0.1166 == 0.78, which doesn't quite hold in the arithmetic that I was taught... Rather the Effect/Coef ratio is about 6.69 on both the effect and its SE, so I think it is a fair guess (being too lazy to check the actual code) that Low and High columns define the full range of ages, not the quartiles. -pd > In the presence of interactions you should not be looking at the > coefficients, but rather at the predictions. > > ?Predict > > -- > David. > > >> >> Best regards, >> Sebastian >> >> ______________________________________________ >> 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. > > 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. -- Peter Dalgaard, Professor Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ 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.
