Solved – Response variable: percentage and too many zeros (zero inflated Poisson?)

I am analysing the effect of density (categorical), gonad mass (continuous) and temperature (continuous) on the percentage of acini spawning in a gonad. My replicate unit is a scallop.

As my response variable is a percentage, and I have many zeros, I was wondering if a zero inflated Poisson regression would be adequate. I know this is used for count data – but as my data is percentage I am wondering if it would be all right to use this model.

The difficulty with the Poisson is that it is defined on the integers; you're dealing with a fraction between 0 and 1.

If you have percentages, presumably you have the numerator and the denominator of that percentage, in which case you might normally look at something more like logistic regression.

This then suggests that a corresponding zero-inflated model would be zero-inflated binomial.

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