Hello,

I'm having a problem to fit a model with lmer. I would like to know if there
is a way to fit a lmer model with no fixed effects terms (a model without
coefficients of fixed effects).

I'm trying to analyze a dataset in a way that I'm having this problem. I'm
comparing the efficiency of two trap types in the capture of small mammals,
using binomial models with each capture as the sampling unities and the trap
type (a or b) as the binary response variable (allowing to put the
individuals as one of the random effects, once we have recapture data). To
do this, I'm trying to fit a model without fixed effects and whose intercept
is given as the proportion of the trap b (the trapping effort, given as an
offset term), and then comparing this model with another whose intercept is
calculated according to the proportion of captures in the trap b (also
without fixed effects, but with intercept calculated by the algorithm).

The problem is to fit the first model, with no fixed effects and intercept
given: lmer(formula= trap ~
offset(rep(log(0.6875/(1-0.6875)),length(dados$trap))) -1 + (1|session) +
(1|grid/individual) , family=binomial, data=dados)

--Where "0.6875" is the trapping effort of trap b, "session" is the sampling
session (21 sampling sessions), "grid" is the sampling grid (3 sampling
grids), "individual" is the individual ID, and the hierarchy
"grid/individual" is because there is no movement of individuals between
grids.

I found a discussion forum of 2007 where this topic were discussed, but I
couldn't find an answer. So I would like to know if someone knows a way to
fit this type of model. If the answer is that there is no way to do this, I
would like to know if someone knows another way to fit a binomial
mixed-effects model with no fixed effects.

Thank you everybody.

Bruno.

-- 
Bruno Trevizan Pinotti
Coordenador de projetos e especialista em mastofauna
Mestre em Zoologia pela Universidade de São Paulo
Instituto de Biociências - Departamento de Zoologia
CRBio 72457/01-D
Tel (11)3735-6061
Cel (11)7503-9099

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