[R] What is the degrees of freedom in an nlme model

[Jun Shen]

Dear all,

I want to do a F test, which involves calculation of the degrees of
freedom for the residuals. Now say, I have a nlme object "mod.nlme". I
have two questions

1.How do I extract the degrees of freedom?
2.How is this degrees of freedom calculated in an nlme model?

Thanks.

Jun Shen

Some sample code and data
=================================================================
mod.nlme<-nlme(RESP~E0+(Emax-E0)*CP**gamma/(EC50**gamma+CP**gamma),data=Data,
fixed=E0+Emax+gamma+EC50~1,
random=list(pdDiag(EC50+E0+gamma~1)),
groups=~ID,
start=list(fixed=c(E0=1,Emax=100,gamma=1,b=50))
)

The "Data" object
structure(list(ID = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,
2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L,
3L, 3L, 3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L, 4L,
4L, 4L, 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 5L,
5L, 5L, 5L, 5L, 5L, 5L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L,
6L, 6L, 6L, 6L, 6L, 6L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L,
7L, 7L, 7L, 7L, 7L, 7L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L,
8L, 8L, 8L), CP = c(1, 2, 3, 4.5, 5, 7.5, 11.25, 12, 18, 30,
45, 60, 90, 120, 150, 200, 1, 2, 3, 4.5, 5, 7.5, 11.25, 12, 18,
30, 45, 60, 90, 120, 150, 200, 1, 2, 3, 4.5, 5, 7.5, 11.25, 12,
18, 30, 45, 60, 90, 120, 150, 200, 1, 2, 3, 4.5, 5, 7.5, 11.25,
12, 18, 30, 45, 60, 90, 120, 150, 200, 1, 2, 3, 4.5, 5, 7.5,
11.25, 12, 18, 30, 45, 60, 90, 120, 150, 200, 1, 2, 3, 4.5, 5,
7.5, 11.25, 12, 18, 30, 45, 60, 90, 120, 150, 200, 1, 2, 3, 4.5,
5, 7.5, 11.25, 12, 18, 30, 45, 60, 90, 120, 150, 200, 1, 2, 3,
4.5, 5, 7.5, 11.25, 12, 18, 30, 45, 60, 90), RESP = c(3.19, 2.52,
2.89, 3.28, 3.82, 7.15, 11.2, 16.25, 30.32, 55.25, 73.56, 82.07,
89.08, 95.86, 97.97, 99.03, 3.49, 4.4, 3.54, 4.99, 3.81, 10.12,
21.59, 24.93, 40.18, 61.01, 78.65, 88.81, 93.1, 94.61, 98.83,
97.86, 0.42, 0, 2.58, 5.67, 3.64, 8.01, 12.75, 13.27, 24.65,
46.1, 65.16, 77.74, 87.99, 94.4, 96.05, 100.4, 2.43, 0, 6.32,
5.59, 8.48, 12.32, 26.4, 28.36, 43.38, 69.56, 82.53, 91.36, 95.37,
98.36, 98.66, 98.8, 5.16, 2, 5.65, 3.48, 5.78, 5.5, 11.55, 8.53,
18.02, 38.11, 58.93, 70.93, 85.62, 89.53, 96.19, 96.19, 2.76,
2.99, 3.75, 3.02, 5.44, 3.08, 8.31, 10.85, 13.79, 32.06, 50.22,
63.7, 81.34, 89.59, 93.06, 92.47, 3.32, 1.14, 2.43, 2.75, 3.02,
5.4, 8.49, 7.91, 15.17, 35.01, 53.91, 68.51, 83.12, 86.85, 92.17,
95.72, 3.58, 0.02, 3.69, 4.34, 6.32, 5.15, 9.7, 11.39, 23.38,
42.9, 61.91, 71.82, 87.83)), .Names = c("ID", "CP", "RESP"), class =
"data.frame", row.names = c(NA,
-125L))