Message-ID: <528A6F81.5080003@gmail.com>
Date: 2013-11-18T19:50:25Z
From: Gustaf Granath
Subject: Set individual variance components to zero in lme
Hi,
Is it possible to set individual variance components in lme() to zero?
For example, say that you have 4 different locations and and you
estimate individual variance components at each location + separate
residual variances.
lme( y ~ location, random = ~ 0 + location|plot/plant, data = dat,
weights = varIdent(form = ~1|location) )
Now I want to test if the plot variance component at location x is
greater than zero. I can do this by fitting individual models.
lme( y ~ 1, random = ~ 1|plot/plant, data = dat, subset = location=="x"
) versus
lme( y ~ 1, random = ~ 1|plant, data = dat, subset = location=="x" )
using a LRT test. However, it would be convenient if it is possible to
fix individual components to zero in the first model with all locations,
like the G.param argument can do in asreml-r. It doesnt seem like there
is an easy way with lme() but maybe someone has tried it?
Cheers
Gustaf
--
Gustaf Granath (PhD)
Post doc
McMaster University
School of Geography & Earth Sciences