[R-sig-ME] parsimonious mixed models

[Wing Yee Chow]

Hi there, 

I'm trying to follow Bates et al.'s guidelines for parsimonious mixed models
and have two questions:

1.       In reducing (near-zero) variance components from the random effects
structure, is the criterion simply the size of the variance? Or do I need to
keep a simple effect as long as I'm keeping a higher order effect that
involves that factor? That is, with the following random effects structure,
do I take out (i) just cSenttype:cCongruity for item, or (ii) both
cSenttype:cCongruity for item AND cCongruity for subj?

 

Random effects:

Groups   Name                 Variance Std.Dev.

item     cSenttype:cCongruity       0     0.0  

 item.1   cCongruity            205437   453.3  

 item.2   cSenttype             100765   317.4  

 item.3   (Intercept)           124422   352.7  

 subj     cSenttype:cCongruity  134752   367.1  

 subj.1   cCongruity                 0     0.0  

 subj.2   cSenttype              87161   295.2  

 subj.3   (Intercept)          2434746  1560.4  

 Residual                      4891977  2211.8  

Number of obs: 1082, groups:  item, 48; subj, 24

 

2.       In another dataset, I have a 3 x 2 within-participant and
within-item design. I specified the contrasts for the two factors in this
way:

contrasts(tempdata$congruity) <- contr.sum(2)/2

contrasts(tempdata$sentencetype)=cbind("AvsBC" = c(-2/3, 1/3, 1/3), "BvsC" =
c(0, -1/2, 1/2))

 

I got the model matrix (mmatrix) from the maximal model (m0) to construct
the zero-correlation parameter model (m1). I think I know how to do this for
a factor with two levels (i.e., only one contrast), but I'm not sure about
the current case since I have both cSenttypeAvsBC and cSenttypeBvsC for the
3-level factor sentencetype. Is this the right syntax?

 

cSenttypeAvsBC <- mmatrix [,2] # columns 2 and 3 encode different contrasts
of sentencetype

cSenttypeBvsC <- mmatrix[,3]

cCongruity <- mmatrix[,4]

m1<- lmer(value ~ sentencetype * congruity + ((cSenttypeAvsBC +
cSenttypeBvsC) * cCongruity||subj) + ((cSenttypeAvsBC + cSenttypeBvsC) *
cCongruity||item), REML=FALSE,

                          data=tempdata)

 

Many thanks!!

Wing-Yee Chow


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