[R] SE estimates for treatment groups from nlme

Katherine A Grieve grieve at u.washington.edu
Mon Apr 10 19:20:03 CEST 2006

I have looked at that example on p. 373, however it still does not help me to
  get the stand errors i need. In my case, with the 18 different groups, I am 
combining more than just the (intercept) term with one other row in the Summary 
tTable. It is no problem to form linear combinations of the coefficients, but 
the SE in the tTable cannot just be combined. Similarly, intervals just gives me
  CI for each entry (row) in the tTable but these are not the group estimates 
that I am looking for.

An example to illustrate what i mean the rows of the tTable would be labeled 
something like this (A=2 levels, B=3 levels, C=3 levels):
Fixed Effects: (Asym~A*B*C)
                   Value      SE
Asym.(intercept)    x1
Asym.A1             x2
Asym.B1             x3
Asym.B2             x4
Asym.C1             x5
Asym.C2             x6
Asym.A1B1           x7
Asym.A1B2           x8
Asym.A1C1           x9
Asym.A1C2           x10
Asym.B1C1           x11
Asym.B2C1           x12
Asym.B1C2           x13
Asym.B2C2           x14

So, to get an estimate for the groups I form linear combinations e.g.:
Group A2,B1,C1 = x1 + x3 + x5 + x11

I am combining 4 coefficients to get the group mean -- is there a way to 
get the corresponding SE. It is definitely not a linear combination of the SE
listed in the tTable.
And, intervals just gives me a CI for each entry (row) in the table, not the 
linear combinations which form my groups.

Thanks again.
It's a bit of fiddling, but there is an example coming close to what you want 
on page 373 of Pinheiro/Bates, and in file \library\nlme\scripts\ch08.R, 
section 8.2. And don't forget that you can use "intervals" on nlme-results.

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