[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), rep(0,17), fixef(ETR.nlme), 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.
Quantitative Ecology and Resource Management
University of Washington
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