Dear R users, I am using 'R' version 2.2.1 and 'S-PLUS' version 6.0; and I loaded the MASS library in 'S-PLUS'.
I am running a logistic regression using glm: --------------------------------------------------------------------------- > mydata.glm<-glm(COMU~MeanPycUpT+MeanPycUpS, family=binomial, data=mydata) --------------------------------------------------------------------------- The values in summary(mydata.glm) are identical for 'R' and 'S-PLUS' (except that S-PLUS does not return an AIC value). Here is the summary(mydata.glm): ------------------------------------------------------------------- >summary(mydata.glm) Call: glm(formula = COMU ~ MeanPycUpT + MeanPycUpS, family = binomial,data = mydata) Deviance Residuals: Min 1Q Median 3Q Max -2.3514 -0.8268 -0.4831 0.8866 1.9864 Coefficients: Estimate std.Error z value Pr(>|z|) (Intercept) 75.482 41.616 1.814 0.0697 . MeanPycUpT 1.143 2.867 0.399 0.6902 MeanPycUpS -2.548 1.225 -2.081 0.0374 * --- Signif.codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 (Dispersion parameter for binomial family taken to be 1) Null deviance: 30.316 on 21 degrees of freedom Residual deviance: 23.900 on 19 degrees of freedom AIC: 29.9 -------------------------------------------------------------------- When I use the 'AIC' and the 'logLik' command in 'R' and 'S-PLUS' I get different values: 'R' ----------------- > AIC(mydata.glm) [1] 29.89986 > logLik(mydata.glm) 'log Lik.' -11.94993 (df=3) ----------------- 'S-PLUS' ----------------- > AIC(mydata.glm) [1] 71.03222 > logLik(mydata.glm) [1] -31.51611 ----------------- However, if I use the 'extractAIC' command in 'S-PLUS' the returned value is the same as the one in 'R'. 'R' ------------------------ > AIC(mydata.glm) [1] 29.89986 > extractAIC(mydata.glm) [1] 3.00000 29.89986 ------------------------- 'S-PLUS' ------------------------ > extractAIC(mydata.glm) [1] 3.00000 29.89986 ------------------------ ***************************************************** MY QUESTIONS ARE: 1) Which AIC value is the correct one? 2) Which log-likelihood value is the correct one? 3) If 'extractAIC' in 'S-PLUS' and all values in 'R' are the correct ones, and the 'AIC' and 'logLik' in 'S-PLUS' values are wrong then: Why 'S-PLUS' cannot retrieve a log-likelihood value from my glm object('mydata.glm'), even though it is using log-likelihood to calculate its residual deviance? ******************************************************* Thank you for you time and Kind attention. Sincerely, Leandra de Sousa -------------------------------------- Ph.D Candidate School of Fisheries and Ocean Sciences Universisty of Alaska Fairbanks 245 O'Neill Bldg. Fairbanks, AK 99775 e.mail: [EMAIL PROTECTED] ______________________________________________ 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.