Jennifer, Please provide us more information. It would be helpful to see the actual code you ran along with the actual output. How did you get the values that your included with your email message? Did you get the values using the summary function, e.g.
> fit0<-lm(y~x+sex+x*sex) > summary(fit0) Call: lm(formula = y ~ x + sex + x * sex) Residuals: Min 1Q Median 3Q Max -108.6049 -29.9293 -0.3111 27.8004 165.3499 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 8.62361 8.55021 1.009 0.314 x 3.88322 0.07252 53.548 <2e-16 *** sex -11.78652 12.56677 -0.938 0.349 x:sex 1.22804 0.10882 11.285 <2e-16 *** --- Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 or some other way? John John David Sorkin M.D., Ph.D. Chief, Biostatistics and Informatics University of Maryland School of Medicine Division of Gerontology Baltimore VA Medical Center 10 North Greene Street GRECC (BT/18/GR) Baltimore, MD 21201-1524 (Phone) 410-605-7119 (Fax) 410-605-7913 (Please call phone number above prior to faxing)>>> Jennifer Hou <jennifer....@hotmail.de> 8/4/2010 4:22 PM >>> Hello, I have got a linear model that looks like this: lm(criterion ~ variable.A*variable.a + variable.B*variable.b + variable.C *variable.c) The output computed with stdCoeff() seems to be all right, but it does not show the coefficients of the interaction of the first pair of variables. Instead, it shows "NA": (Intercept) NA variable.A 0.0925094150 variable.a 0.1517246479 variable.B -0.0023847092 variable.b 0.0256653197 variable.C 0.0194313471 variable.c 0.0192897539 variable.A : variable.a NA variable.B : variable.b 0.0471111439 variable.C : variable.c 0.0696702457 This happens with all my data frames, there is always a problem with the first pair of variables. Does anyone have an idea why R does not compute the coefficients of "variable.A : variable.a"? Thanks in advance! Best regards, Jennifer [[alternative HTML version deleted]] ______________________________________________ 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. Confidentiality Statement: This email message, including any attachments, is for th...{{dropped:6}} ______________________________________________ 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.