error while trying to get predictions from a lme object

Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) :
  contrasts can be applied only to factors with 2 or more levels

---------- Forwarded message ----------
From: Antonio P. Ramos <ramos.grad.student at gmail.com>
Date: Fri, May 25, 2012 at 5:29 PM
Subject: error while trying to get predictions from a lme object
To: Antonio Pedro Ramos <ramos.grad.student at gmail.com>


Another example of the error I am taking about:

# the variables from this models dependens
model <- lme(log(child_mortality) ~ as.factor(cluster)*time +

+              my.new.time.one.transition.low.and.middle + ttd +
+              maternal_educ+ log(IHME_id_gdppc) + hiv_prev-1,
+              merged0,na.action=na.omit,method="ML",weights=varPower(form
= ~ time),
+              random= ~ time| country.x,
+              correlation=corAR1(form = ~ time),
+              control=lmeControl(msMaxIter = 200, msVerbose = TRUE))

# create a toy data set
test.pred0 <-

 expand.grid(time=20:29,country.x=c("Poland","Brazil","Argentina"))

z0 <-

as.data.frame(cbind(my.new.time.one.transition.low.and.middle=c(0,0,0,0,0,0,1,2,3,4),
+       ttd=c(0,0,0,0,0,0,1,0,0,0),
+       maternal_educ=seq(from=10.0, to=12.0, length.out=10),
+       IHME_id_gdppc=log(seq(from=5000, to=8000, length.out=10)),
+       hiv_prev=rep(.005,10),cluster=rep("One Transition, Middle
Income",10)))

z <- rbind(z0,z0,z0)
test.pred <- cbind(test.pred0,z)
# check
head(test.pred)

  time country.x my.new.time.one.transition.low.and.middle ttd
 maternal_educ    IHME_id_gdppc hiv_prev
1   20    Poland                                         0   0
  10 8.51719319141624    0.005
2   21    Poland                                         0   0
10.2222222222222 8.58173171255381    0.005
3   22    Poland                                         0   0
10.4444444444444 8.64235633437024    0.005
4   23    Poland                                         0   0
10.6666666666667 8.69951474821019    0.005
5   24    Poland                                         0   0
10.8888888888889 8.75358196948047    0.005
6   25    Poland                                         0   0
11.1111111111111 8.80487526386802    0.005
                        cluster
1 One Transition, Middle Income
2 One Transition, Middle Income
3 One Transition, Middle Income
4 One Transition, Middle Income
5 One Transition, Middle Income
6 One Transition, Middle Income

# run the predictions

predict(model,test.pred,level=0)

Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) :
  contrasts can be applied only to factors with 2 or more levels

Thank you!

Antonio Pedro.

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