A couple basic questions

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A couple basic questions

Postby dbuhl » Mon Nov 25, 2019 5:13 pm

I have a couple questions that I cannot seem to find information on.

1) Any sample size recommendations I find have to do with how many sites and how many surveys there should be. What I would like to know is given a particular design and sample size, how many parameters can I estimate without overfitting. For example, I have 100 sites and 5 surveys at each site. One rule of thumb that is common is 1 parameter per 10 sites. In logistic, I have seen this modified to 1 parameter per 10 detections. It seems like that rule would be more appropriate for occupancy analysis. So in my example of 100 sites and 5 surveys, how many parameters can I estimate if the species was present at 80% of the sites with a detection probability of 0.8? Or what if I only observed my species at 10% of the 100 sites with a detection probability of 0.20, then how many parameters can I estimate?

2) If you have covariates with levels that have no detections, is this a problem? For example, I have a covariate for region, but my species was only seen in 2 of the 3 regions so for the 3rd region the detection history is all zeros. In logistic regression, this would be a problem. What I can't figure out is if it is a problem in occupancy analysis. I ran a couple simulations to try and figure it out and in those simulations I found that if the covariate was used to model detection, it resulted in huge standard errors like what would happen in logistic regression. But, if the covariate was used to model occupancy, it did not seem to have any problems.

Any insight on either of these questions would be greatly appreciated. Thank you.
dbuhl
 
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