Hi Eva, A couple questions: Are repeated measurements taken on rnr? Is rnr "subject"? Is stress a continuous variable?
See below. On Dec 11, 2006, at 11:04 AM, Fucikova, Eva wrote: > Dear All, > > > > I am working with linear mixed-effects models using the lme4 > package in > R. I created a model with the lmer function including some main > effects, > a two-way interaction and a random effect. Now I am searching how I > could incorporate an interaction between the random effect and one of > the fixed effects. > > > > I tried to express the interaction in: > > recap_random3<-lmer(breath~handling+stress+stress:handling+(1|rnr) > +(0|rn > r:stress)) > lmer will want rnr:stress to be a factor, but (0|factor) doesn't make sense. To test for random variation in slopes, you want (stress | rnr), (or (1|rnr) + (0+stress | rnr) for uncorrelated slopes). > however R gives me the following error message > > : > > Error in eval(expr, envir, enclos) : fl[[2]] must be a factor of > length > 1744 > > In addition: Warning messages: > > 1: numerical expression has 1744 elements: only the first used in: > rnr:stress > > 2: numerical expression has 1744 elements: only the first used in: > rnr:stress > > > > If I fit this model in SPSS, this gives me output, but I don't know > whether I can trust that. > > > > > > Therefore I went to look for an alternative: > > After looking at the help function in R for lmer I deduced these > models. > > > Examples from R > > (fm1 <- lmer(Reaction ~ Days + (Days|Subject), sleepstudy)) > (fm2 <- lmer(Reaction ~ Days + (1|Subject) + (0+Days|Subject), > sleepstudy)) > anova(fm1, fm2) > > > > > > My models would then look like this: > > > > recap_random0<-lmer(breath~handling+stress (1|rnr)) > > recap_random1<-lmer(breath~handling+stress (1|rnr)+(0+stress|rnr)) > Or rather with a plus sign > > recap_random0<-lmer(breath~handling+stress + (1|rnr)) > > recap_random1<-lmer(breath~handling+stress + (1|rnr)+(0+stress|rnr)) or > > recap_random0<-lmer(breath~handling+stress (stress | rnr)) > > > However, I do not know how to interpret the results. Does the model > see > stress|rnr as an interaction between stress and rnr, or did it take > stress nested in rnr. > > > >> summary(recap_random1) > > Linear mixed-effects model fit by REML > > Formula: breath ~ handling + stress + stress:handling + (1 | rnr) + > (0 + > stress | rnr) > > AIC BIC logLik MLdeviance REMLdeviance > > 9748 9781 -4868 9719 9736 > > Random effects: > > Groups Name Variance Std.Dev. > > rnr (Intercept) 55.6711 7.4613 # BUT > > rnr stress 15.2805 3.9090 # Does > this > output line express the interaction??? > If the model statement was correct, these would be variances associated with the intercepts and slopes of different levels of rnr. Thus, I would call that rnr by stress interaction. Cheers, Hank > Residual 7.4567 2.7307 # If not, how > should the interaction output look like? > > number of obs: 1744, groups: rnr, 217; rnr, 217 > > > > Fixed effects: > > Estimate Std. Error t value > > (Intercept) 28.164471 0.716359 39.32 > > handling 0.012477 0.012330 1.01 > > stress 0.636979 0.416011 1.53 > > > > Correlation of Fixed Effects: > > (Intr) hndlng stress > > handling -0.645 > > stress -0.517 0.667 > > > > > > Could anybody please give me an advice how to solve this problem? > Which > way is correct to express interaction in the random factors? How > should > the output look like? > > > > Thank you in advance, > > Eva Fucikova > > > > ******************************************** > > Msc. Eva Fucikova > Netherlands Institute of Ecology (NIOO-KNAW) > PO Box 40 > 6666 ZG Heteren > The Netherlands > tel.: +31 (0)26 4791248 > Email:[EMAIL PROTECTED] > > ******************************************* > > > > > [[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. Hank Stevens, Assistant Professor 338 Pearson Hall Botany Department Miami University Oxford, OH 45056 Office: (513) 529-4206 Lab: (513) 529-4262 FAX: (513) 529-4243 http://www.cas.muohio.edu/~stevenmh/ http://www.muohio.edu/ecology/ http://www.muohio.edu/botany/ "E Pluribus Unum" If you send an attachment, please try to send it in a format anyone can read, such as PDF, text, Open Document Format, HTML, or RTF. Please try not to send me MS Word or PowerPoint attachments- Why? See: http://www.gnu.org/philosophy/no-word-attachments.html ______________________________________________ [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.
