Linear mixed effects models are highly flexible in handling a broad range of
data types and are therefore widely used in applications. A key part in the
analysis of data is model selection, which often aims to choose a parsimonious
model with other desirable properties from a possibly very large set of
candidate statistical models. Over the last 5-10 years the literature on model
selection in linear mixed models has grown extremely rapidly. The problem is
much more complicated than in linear regression because selection on the
covariance structure is not straightforward due to computational issues and
boundary problems arising from positive semidefinite constraints on covariance
matrices. To obtain a better understanding of the available methods, their
properties and the relationships between them, we review a large body of
literature on linear mixed model selection. We arrange, implement, discuss and
compare model selection methods based on four major approaches: information
criteria such as AIC or BIC, shrinkage methods based on penalized loss
functions such as LASSO, the Fence procedure and Bayesian techniques.Comment: Published in at http://dx.doi.org/10.1214/12-STS410 the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org