[R-meta] Help computing effect size of two-choice test (binary response)

[Nathalia Ximenes Gonçalves]

Hello everyone,

I'm conducting a meta-analysis about chemical defenses effectiveness. I'm
facing a problem with a set of studies and I was wondering if someone could
help me. In some studies, the experiment was conducted in a two-choice
test, in which the predator had to choose a prey with chemical defense or a
prey without chemical defense. For instance, if the experiment had 20
predators, each one had to choose between two types of prey, let's suppose
that 16 predators had choosen prey without chemical defenses and 4
predators had choosen prey with chemical defenses. Therefore, I would have:
'treatment = 4', 'control = 16', and a total sample size of 20. I cannot
use any odds ratio, risk ratio, etc metrics, because I don't have a 2x2
table, and all the results would be equal to zero if I consider a sample
size of 20 for treatment and control separately. Would anyone have any
recommendations for calculating the effect size for this type of study?

Thanks,

Nathalia

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