Dear listers,
I am trying to fit a nlme model with "age" and "pds" as reals, and
"zone" a factor with two levels "Annaba" and "Boumalek" . The "best"
model found is the following:
> modm3
Nonlinear mixed-effects model fit by maximum likelihood
Model: pds ~ Asym/(1 + exp((xmid - age)/scal))
Data: croispulm
Log-likelihood: -91.86667
Fixed: list(Asym ~ zone, xmid ~ zone, scal ~ 1)
Asym.(Intercept) Asym.zoneBoumalek xmid.(Intercept)
xmid.zoneBoumalek scal
9.99551079 0.39423966 4.97981027
0.06969807 2.23116661
Random effects:
Formula: list(Asym ~ 1, xmid ~ 1)
Level: nichoir
Structure: General positive-definite, Log-Cholesky parametrization
StdDev Corr
Asym.(Intercept) 1.796565e-06 As.(I)
xmid.(Intercept) 1.219400e-04 0
Residual 6.163282e-01
Correlation Structure: Continuous AR(1)
Formula: ~age | nichoir
Parameter estimate(s):
Phi
0.3395242
Number of Observations: 102
Number of Groups: 17
Everything normal so far.
Things come to be strange when I try to compute predicted values:
> pred<-predict(modm3,newdata=mydata,type="response")
Error in predict.nlme(modm3, newdata = mydata, type = "response") :
Levels Annaba,Boumalek not allowed for zone
I have checked and re-checked that zone in the newdata is well a factor
with the "good" levels, and I can hardly understand why these two levels
used when fitting the model are now rejected when used for computing
predicted values.
Any hint welcome,
Best regards,
Patrick
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