Yannan Jiang wrote: > Hi there, > > > > I am trying to run simulations using R with linear mixed model (lme). There > are two factors in my fixed effect model, educ (treatment and control) and > mth (visit 1, 2, and 3). What I want to obtain is the estimated treatment > difference (treatment - control) at visit 3, plus the standard error and > p-value. This can be easily obtained in SAS using lsmeans or estimate > statements, but I am not sure how to do this in R. > > > > The fixed effects I obtained are as follows: > > > > Fixed effects: ymth ~ educ * mth - 1 > > Value Std.Error > DF t-value p-value > > educcont 0.14814308 0.006232419 93 > 23.769758 0.0000 > > eductreat 0.13696952 0.006255672 93 > 21.895254 0.0000 > > mthymth2 0.00003759 0.006333043 165 > 0.005936 0.9953 > > mthymth3 0.01075489 0.006251328 165 > 1.720416 0.0872 > > eductreat:mthymth2 0.00323847 0.008947291 165 > 0.361950 0.7179 > > eductreat:mthymth3 -0.01246565 0.008941306 165 > -1.394164 0.1651 > > > > > > The estimated treatment difference I am interested are: > > > > a<-0.14814308+0.01075489 > > b<-0.13696952+0.01075489-0.01246565 > >> b-a > > [1] -0.02363921 (treatment effect at visit 3, same as SAS lsmean output) > > > > But I don't know how to get the standard error and corresponding p-value for > this estimate. Any of your helps on that would be greatly appreciated!
How about fitting the model this way? df$mth <- relevel(df$mth, ref = "ymth3") lme(ymth ~ educ * mth, random = ~ 1 | id, data = df) The coefficient for educ will contain the simple effect of educ at mth=ymth3, along with a standard error and p-value. > Thanks, > > Yannan > > > > > [[alternative HTML version deleted]] > > ______________________________________________ > [email protected] 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. -- Chuck Cleland, Ph.D. NDRI, Inc. 71 West 23rd Street, 8th floor New York, NY 10010 tel: (212) 845-4495 (Tu, Th) tel: (732) 512-0171 (M, W, F) fax: (917) 438-0894 ______________________________________________ [email protected] 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.
