[R-sig-ME] mixed model with recapture data

[Leandro Rabello Monteiro]

Dear All
 I am trying to evaluate the body condition (SMI) of bats in a
mark-recapture study, in response to lesions caused by arm bands.
Because recapture is a matter of chance, the design is highly
unbalanced. Most individuals were recaptured twice, but there can be
up to 18 recaptures in a period of 4 years.

The data set is formatted in a way that each line is one individual at
a point in time. The head() of the data frame looks like this

  ID Sex      SMI MarkR YearMonth
1  1   M 15.10700    L0   2013-04
2  1   M 14.52348    L0   2013-06
3  1   M 15.51033    L0   2013-07
4  1   M 15.51033    L0   2013-09
5  1   M 15.26151    L0   2013-11
6  1   M 15.33953    L0   2014-08

ID is a factor to identify individuals, MarkR (response to banding) is
a factor with levels (NR =  no ring, the first capture, L0 = ringed,
no lesion, L1 = lesion type 1, L2 = lesion type 2). A single
individual can change its level in MarkR, so it is a within-subject
fixed factor. Some individuals will develop lesions and some will not.
The question of interest is whether banding itself or lesions caused
by banding can be associated with lower SMI, so the only comparisons
of interest are the levels L0-2 against the "control" NR.

 Lesions, particularly L2 are rare, occurring in ~3% of observations
(out of 2400), again with a high unbalance among levels. There is some
seasonality in body condition, but I am not particularly interested in
this aspect right now, but I am not sure about the best way to include
the temporal factor YearMonth it in the model.

I have tried the following, using individuals and YearMonth as random effects.
lm.smi<-lmer(SMI~Sex*MarkR+(1|ID)+(1|YearMonth),data=smi)

I would appreciate some guidance as to whether I might be missing
something relevant, particularly due to the highly unbalanced design.
I have searched a lot but have not managed to find similar examples in
the literature or the web. Thanks a lot for your time.


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Leandro R. Monteiro
Laboratorio de Ciencias Ambientais
Universidade Estadual do Norte Fluminense
E-mail: lrmont using uenf.br
CV Lattes: http://lattes.cnpq.br/4987216474124557
WS: https://sites.google.com/uenf.br/ecol-evolucao-de-mamiferos/
English WS: https://sites.google.com/uenf.br/mammalecologyandevolution/
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