[R] Random specification in LMER
spencer.graves at pdf.com
Fri Apr 14 23:52:57 CEST 2006
Arnaud Ghilain wrote:
> Can anybody help me understand the difference between the three different codes
> in specifying the slope in the random part of a mixed model using LMER?
> Here are the codes:
> (age | id)
> (1 + age | id)
SG: These to are the same: For each level of "id", both estimate
random deviations for intercept and slope for age plus a covariance
matrix for these two random parameters.
> (age - 1 | id)
SG: For each level of "id", this estimates only a random deviation for
slope for age plus a variance for that random slope.
SG: "(1|id)+(age-1|id)": For each level of "id", this estimates a
random deviation for both intercept and slope for age plus a variance
for each term assuming their covariance is 0.
SG: See Douglas Bates (2005) "Fitting linear mixed models in R", R
News, 5(1):27-30 ("www.r-project.org" -> Documentation: Newsletter).
Also, if you haven't already done this, you might want to review the
vignette in library(MlmRev).
hope this helps.
> Thank you in advance
> R-help at stat.math.ethz.ch mailing list
> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
More information about the R-help