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lme varFix under ML fit does not match coefficients standard error

Vaida, Florin 
Hello all,

This is probably known, but it?s news to me: the standard errors printed for the lme model fit run under method=?ML? are in fact those computed under method=?REML?.
Is this the expected behavior?  And if so, are there any reasons for this choice?
Reproducible example below.

Thanks,
Florin

library(nlme)
fit.reml =  lme(log(conc) ~ Time, random=~1|Subject, data=Glucose, na.action=na.omit, method="REML")
(se.reml = summary(fit.reml)$tTable[,2])
## (Intercept)        Time
## 0.019457141 0.005829144
(se.reml = sqrt(diag(summary(fit.reml)$varFix)))
## (Intercept)        Time
## 0.019457141 0.005829144
fit.ml =  lme(log(conc) ~ Time, random=~1|Subject, data=Glucose, na.action=na.omit, method="ML")
(se.ml = summary(fit.ml)$tTable[,2]) # they match the REML SE?s
## (Intercept)        Time
## 0.019457141 0.005829144
(se.ml = sqrt(diag(summary(fit.ml)$varFix))) # they do not match the tTable SE?s
## (Intercept)        Time
## 0.019405324 0.005813621

Thread (8 messages)

Vaida, Florin lme varFix under ML fit does not match coefficients standard error Feb 18 Ben Bolker lme varFix under ML fit does not match coefficients standard error Feb 18 Rolf Turner lme varFix under ML fit does not match coefficients standard error Feb 18 Ben Bolker lme varFix under ML fit does not match coefficients standard error Feb 18 Vaida, Florin lme varFix under ML fit does not match coefficients standard error Feb 20 Dimitris Rizopoulos lme varFix under ML fit does not match coefficients standard error Feb 20 Vaida, Florin lme varFix under ML fit does not match coefficients standard error Feb 20 Ben Bolker lme varFix under ML fit does not match coefficients standard error Feb 20