[R-sig-eco] Proper treatment of Proportion Response Data with Two Categorical Predictors

[Everett]

Hello,

I believe I have exhausted my online resources (and eyes) in trying to
determine the appropriate method of analysis for the following
investigation.

I wish to determine if the efficiencies (% recovery) of two sampling units
are significantly different. I sampled in three different fields. I
attempted to collect 12 samples per unit per field (2 x 12 x 3 = 72);
however, some sample sites had no seeds and resulting data were excluded (so
as to not confuse with 'true' zero data; i.e., 0 seeds of x recovered).
Working sample size = 24 and 27 (51), per unit.

My dataset sets up like this:

1) 51 observations 
2) Response variable = percent seeds recovered; x = 0-1
3) Predictor variable 1 = unit (K or L); fixed categorical
4) Predictor variable 2 = field (1, 2, or 3); random categorical

More than 50% of my data are zeros, therefore, the distribution is far from
normal.

Can someone provide guidance RE how best to proceed? Thank you kindly in
advance.

-Everett




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