[R-sig-ME] GLMM -Firefly Flash

Thierry Onkelinx thierry.onkelinx at inbo.be
Wed Nov 23 10:27:00 CET 2016

Dear Vickly,

I assume you have measurements on the individual animals and you can
identify the animal during the different exposures. I think you want a
model like this: flash_rate ~ treatment * exposure + temperature + humidity
+ size_ratio + (1|animal_id) This requires -1 + 4 * 3 + 1 + 1 + 1 + 1 = 15
parameters. You have 78 * 3 = 234 observations. That is 234 / 15 = 15.6
observations per parameter, which reasonable to fit the model.

Best regards,

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to say
what the experiment died of. ~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data. ~ Roger Brinner
The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey

2016-11-22 18:01 GMT+01:00 Vickly Mobilim <vickmoe7 op gmail.com>:

> Greetings,
> I've read several writing of yours about GLMM and I thought it would be the
> best tool to answer my research questions. However, I wasn't sure if I
> really need it and my data permit me to use it. That said, I have 78
> individuals of firefly divided into four groups (A= 20 indv., B = 20 indv.,
> C = 20 indv. and D = 18 indv.). This is due to several limitations that I
> can't take more samples of firefly. I will explain the details of the
> experiment below.
> I'm hoping that you can advise me on this issue, whether you have seen such
> cases of low sample size using GLMM or whether GLMM is not suitable for my
> study.
> I expose the fireflies with several intensity of white light according to
> their group (Group A = 0.05lux, B = 0.1lux, C = 0.3lux and D = 0.5lux) then
> measure their flash rates and duration before, during and after exposure to
> light (repeated measure design). Temperature, humidity and individual
> eye-to-body size ratio were also measured. My main aim was to measure the
> impact of several light pollution intensity to their flash rates and
> duration and taking temperature, humidity and eye-to-body size into
> account.
> I realized that calculating changes in their flash rates and duration are
> achievable by subtracting post-experiment result with pre-experiment result
> then use unpaired t-test to compare the results. However, my data was not
> normal and I used Mann-Whitney U test instead. But this does not take
> temperature, humidity and eye-to-body size into account. As I was looking
> into the possibility of taking them into account, I found several modelling
> technique that is suitable including GLMM but I am not sure if I can employ
> them because according to a statistician I am in consult with, the sample
> size is too small to be developed into a model that it would invite more
> problem in analysis.
> --
> Regards,
> Vickly Mobilim
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