Different survival and recapture between Pradel and POPAN?

questions concerning analysis/theory using program MARK

Different survival and recapture between Pradel and POPAN?

Postby bjohn28 » Wed Nov 08, 2017 2:11 pm

Hello,

I am running Pradel Recruitment and Lambda and POPAN models for 2 different populations. For one of these populations, I am getting the same exact survival and recapture probability estimates among all of my top-ranked models:
- Phi(.)p(.)f(time)
- Phi(.)p(.)Lambda(time)
- Phi(.)p(.)pent(time)N(.)
This makes sense to me given that all of these JS formulations "model the recapture of marked animals in the same way". In all 3 of these models, the recapture estimate = 1.00 (95% CI = 1.00-1.00).

For my second population, when I compare the same set of models, I am getting different survival and recapture estimates for the POPAN model only. Recapture from the Pradel models = 0.94 (95% CI = 0.70-0.99), whereas recapture from the POPAN model = 0.99 (95% CI = 0.96-1.00). Survival estimates differ by roughly 1%. I have remade these models from scratch and keep getting the same results.

Could there be an issue with how I am setting up the POPAN model, or is there something inherently different about this model type that I am missing?

Thank you for any help!
bjohn28
 
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Re: Different survival and recapture between Pradel and POPA

Postby Bryan Hamilton » Sat Nov 25, 2017 7:47 pm

Like you, I am running the same dataset through POPAN and Pradel models. I get nearly identical estimates of p (.305 versus .304) but slightly different estimates of phi (.833 versus.851).

I've read through Chapters 12 and 13 of the MARK book several times. I think you are correct that JS and Pradel models estimate p the same way. Pradel models are considered a "special case" of JS models.

Now I initially thought that JS and Pradel models estimate phi the same way. But after re-rereading Chapter 13, Pradel and CJS models actual estimate phi the same way. So you should expect some minor differences in phi between Pradel and POPAN models.

So why are you getting different results for p with the same data and basically the same model? I don't know but it could have something to do with your high recapture values. With recapture estimates of 1 you are at a boundary and the models have trouble with that. If you're recapture rate is really 1, you might consider a different model to get directly at the parameters you are interested in. In other words, you might not need the "nusiance" parameter p.

I would also say a difference of 1% in survival isn't really an issue. I'm not too worried about the difference in survival between my models.
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