[R] SE estimates for treatment groups from nlme

Katherine A Grieve grieve at u.washington.edu
Mon Apr 10 02:10:56 CEST 2006

I am wondering how to obtain SE estimates for fixed effects from a nonlinear mixed effects model? 

I have fixed effects corresponding to three factors A, B and C with 2, 3 and 3 levels respectively. I have fit a model of the following general form:

nlme1<-nlme(y~ SasympOrig(x, Asym, lrc), data=df, fixed=list(Asym~A*B*C, lrc~A*B*C),
	start=c(fixef(ETR.nlme)[1], rep(0,17), fixef(ETR.nlme)[2], rep(0,17))) 

I am using the default ("contr.treatment" and "contr.poly"). The summary table (tTable) gives me the baseline coefficients and a list of differences and I have no trouble calculating the coefficients for any of my treatment groups by forming the correct linear combination of coefficients. However, I don't understand how to obtain the standard errors for these linear combinations from the summary report. What I want to obtain would be 18 parameter estimates with appropriate SEs for my 18 different groups (A*B*C=2*3*3=18).

In response to a similar posting, it was recommended to use the function "estimable" in the package gregmisc. I have looked at this and cannot figure out how to apply it in my situation. Any help would be greatly appreciated.


Katie Grieve
Quantitative Ecology and Resource Management
University of Washington

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