[R-sig-ME] Fwd: What does "number of groups < 50"

[Ben Bolker]

[forwarding to r-sig-mixed models]

-------- Original Message --------
Subject: What does "number of groups < 50"
Resent-Date: Tue, 22 Oct 2013 07:42:08 -0400
Date: Tue, 22 Oct 2013 11:41:04 +0000
From: Maria Paola Bissiri <Maria_Paola.Bissiri at tu-dresden.de>
To: bolker at mcmaster.ca

Dear Prof. Bolker,
I am carrying out an analysis of my data fitting a GLMM with glmer()
(from lme4), family binomial.

In the chapter "pvalues" in the manual (page 59)
http://cran.r-project.org/web/packages/lme4/lme4.pdf
you recommend the starred (*) methods "when the number of groups is < 50".

What is meant exactly with "number of groups"?

I have in total 1548 observations and four groups of perception
experiment participants: German, Chinese, Swedish and English natives
(language is a predictor in the model), with a maximum of 30
participants per language.

Using the starred (*) methods for GLMMs means bootstrapping, but I am
experiencing problems with that (e.g. too long calculation time), so I
would prefer to use Likelihood Ratio Tests.
However, I am not sure if this method is suitable. I am not sure if my
data fulfill the criterium of a number of group > 50, since I do not
know what it means.
=============

      It's not 100% clear since I don't know the structure of your
model exactly (presumably it's something like response ~ [fixed
effects] + (1|participant), or response ~ [fixed effects] +
(?|participant), i.e. you are using participant as a random effect),
but the 'number of groups' is the number of levels of the
random-effects grouping variable, i.e. probably the total number of
participants in your experiment (which sounds like it is probably >
50). These numbers are reported in the output of glmer, in your case
it would look something like "Number of obs: 1548, groups: participant, ??