felix wrote: > Dear all, > > How to obtain the odds ratio (OR) and 95% confidence interval (CI) with > 1 standard deviation (SD) change of a continuous variable in logistic > regression? > > for example, to investigate the risk of obesity for stroke. I choose the > happening of stroke (positive) as the dependent variable, and waist > circumference as an independent variable. Then I wanna to obtain the OR > and 95% CI with 1 SD change of waist circumference.how? > > Any default package(s) or options in glm available now? > > if not, how to calculate them by hand? > > Unless you want to do something advanced like factoring in the sampling error of the SD (I don't think anyone bothers with that), probably the easiest way is to scale() the predictor and look at the relevant line of exp(confint(glm(.....))). As in
(library(MASS); example(confint.glm)) > budworm.lg0 <- glm(SF ~ sex + scale(ldose), family = binomial) > exp(confint(budworm.lg0)) Waiting for profiling to be done... 2.5 % 97.5 % (Intercept) 0.2652665 0.7203169 sexM 1.5208018 6.1747207 scale(ldose) 4.3399952 10.8983903 Or, if you insist on getting asymptotic Wald-statistic based intervals: > exp(confint.default(budworm.lg0)) 2.5 % 97.5 % (Intercept) 0.269864 0.7294944 sexM 1.496808 6.0384756 scale(ldose) 4.220890 10.5546837 You can also get it from the coefficients of the unscaled analysis, like in > budworm.lg0 <- glm(SF ~ sex + ldose, family = binomial) > confint(budworm.lg0) Waiting for profiling to be done... 2.5 % 97.5 % (Intercept) -4.4582430 -2.613736 sexM 0.4192377 1.820464 ldose 0.8229072 1.339086 > exp(confint(budworm.lg0)[3,]*sd(ldose)) Waiting for profiling to be done... 2.5 % 97.5 % 4.339995 10.898390 -- O__ ---- Peter Dalgaard Ă˜ster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ R-help@stat.math.ethz.ch 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.