[R-sig-ME] Looking for help to test the effect of a grouping factor in repeated measures

Léa Fieschi-Méric |e@||e@ch|mer|c @end|ng |rom gm@||@com
Mon Sep 6 16:33:49 CEST 2021


I have a dataset to analyse and I am struggling to build my model set and
was wondering if you could advise me please.

The experimental plan is as follows: several species of animals were
observed for a year, but not regularly (some months have many observations,
others have less). *All individuals belonging to the same species were
housed together in the same terrarium* (unequal number of individuals per
species). The response variable is the number of awake individuals per
terrarium (i.e. per species). The year was divided in 3, unequal, periods
as follows: treatment / control / treatment.

I need to determine the effect of the *Period *(treatment / control), of
the *Species* (12 in total), and of their *Interaction *on the *proportion
of awake animals*. I wanted to use a GLMM with a binomial error
distribution. The problem is that I have repeated measures per species, so
I would like to account for that by using Species as a random effect to
avoid pseudoreplication, but I think I need Species to be a fixed effect
because I want to directly test its effect on my response. Therefore, I
wonder if adding the *Date* (as an integer: number of days since the
beginning of the experiment) to the model does control for these repeated
measures (but I can't use it as a random effect because it is continuous,
and it makes my model too complex to converge when integrated as a fixed
effect), or if I should sum the response per month to use *Month* as a
random effect ordered factor. Or if I could just use a linear model without
bothering, like this: y ~ Treatment * Species !
I am stuck here and would like to avoid taking a mathematically
erroneous approach. Could you advise me please?

I was also wondering what I need to do in order to, in a second phase, be
able to conclude exactly which species were sensitive to the treatment and
which were not?

I am looking forward to hearing back from you, and thank you in advance for
your help!


*Léa FIESCHI-MERIC*, PhD student

Laboratoire d'Ecologie et de Conservation des Amphibiens (LECA)
Freshwater and OCeanic science Unit of reSearch (FOCUS)
Université de Liège (Belgique)
Genetics and Ecology of Amphibians Research Group
Center for Evolutionary Ecology and Ethical Conservation
Laurentian University (Canada)

Tel: (+33) (0) <+32%204%20366%2050%2077>
E-mail: leafieschimeric using gmail.com

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