Hi all,

I'm working on a multi-method (a la Nichols et al. 2008) analysis in PRESENCE and am wondering how I can incorporate a covariate that is specific to the small-scale occupancy parameter (theta).

In my example, the study sites are wetlands where up to 10 amphibians per site are sampled for a pathogen (the number of sampled amphibians is equivalent to the number of 'surveys'). Each individual is sampled three times using tissue samples (equivalent to the number of methods/survey), and the pathogen is either detected (1) or not (0). In this case, the interpretation of theta is the pathogen prevalence (the proportion of infected individuals). I believe this set-up to be appropriate because conditional upon the pathogen occurring at the site (psi), individual amphibians may be infected or uninfected.

Say I have a continuous covariate like the weight of each animal sampled. How would I add this kind of covariate to the input data?

Here are my ideas:

1 - Paste/enter the covariate values directly into the design matrix

2 - Specify the survey covariate as a sampling covariate, but only fill in the first (nSurvey) columns

I think these will work, but I'm wondering if there might be something more efficient out there. Thanks for any thoughts you have.

Brittany