Paul:
I may have found the issue (which is similar to your conclusion). I
checked using egsingle in the mlmRev package as these individuals are
strictly nested in this case:
library(mlmRev)
library(nlme)
fm1 <- lme(math ~ year, random=~1|schoolid/childid, egsingle)
fm2 <- lmer(math ~ year +(1|schoolid:childid) + (1|schoolid), egsingle)
Checking the summary of both models, the output is exactly the same
w.r.t. the fixed effects, variance components, standard errors etc. The
prior two lines of code fit the same models. However, the following does
not generate similar output:
head(coef(fm2)[[1]])
(Intercept) year
2020:273026452 -0.30213394 0.7461233
2020:273030991 0.41469885 0.7461233
2020:273059461 -0.07443003 0.7461233
2020:278058841 0.61676579 0.7461233
2020:292017571 0.29529524 0.7461233
2020:292020281 -1.03811716 0.7461233
> head(coef(fm1, level=2))
(Intercept) year
2020/273026452 0.3248913 0.7461233
2020/273030991 1.0417241 0.7461233
2020/273059461 0.5525952 0.7461233
2020/278058841 1.2437910 0.7461233
2020/292017571 0.9223205 0.7461233
2020/292020281 -0.4110920 0.7461233
Although they are similar for schools:
> head(coef(fm1, level=1))
(Intercept) year
2020 -0.1534565 0.7461233
2040 -0.6985680 0.7461233
2180 -1.0621073 0.7461233
2330 -0.6262567 0.7461233
2340 -1.0090541 0.7461233
2380 -0.6095037 0.7461233
> head(coef(fm2)[[2]])
(Intercept) year
2020 -0.1534566 0.7461233
2040 -0.6985681 0.7461233
2180 -1.0621072 0.7461233
2330 -0.6262567 0.7461233
2340 -1.0090541 0.7461233
2380 -0.6095037 0.7461233
I checked a bit further to see if there was any pattern to the
differences:
tt <- cbind(coef(fm1, level=2)[1], coef(fm2)[[1]][1])
tt$dif <- tt[,1] - tt[,2]
There is clearly a systematic pattern to the difference between the two.
Now, when you go and look at the random effects
head(ranef(fm2)[[2]])
You can see that this is the value that is not being added in to the
coefficients in lmer() and this accounts for the difference. So, these
need to be added in for now.
I hope this helps,
Harold
My question relates to problems that I'm having matching lme and lmer
examples in P&B.
using Matix 0.995
In the Oxide example in p167-170 I can't get the level 2 coefficient
estimates to match the fm1Oxide model in lme is
data(Oxide,package="nlme")
lme(Thickness~1,Oxide)
which I translate in Lmer syntax to
fm3Oxide<-lmer(Thickness~ (1|Lot)+(1|Lot:Wafer),data=Oxide) #or
alternatively which gives the same result
Oxide$LW<-with(Oxide,Lot:Wafer)[drop=TRUE]
fm4Oxide<-lmer(Thickness~ (1|Lot)+(1|LW),data=Oxide)
however if you look at say Lot 8, lme gives
8 1993.767
8/1 1993.677
8/2 1995.170
8/3 1990.693
while lmer gives
coef(fm3Oxide)
....
8 1993.767
8:1 2000.062
8:2 2001.555
8:3 1997.078
To me this looks like lmer in not including the lot random effect (8=
-6.385129, Intercept 2000.153 ). Is this because I'm not specifying the
model correctly?
Thanks Paul
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