POPAN divide by zero error message

questions concerning analysis/theory using program MARK

POPAN divide by zero error message

Postby stshroye » Fri Apr 15, 2022 4:32 pm

I am attempting to estimate abundance of Largemouth Bass sampled by shoreline electrofishing on multiple occasions. Closed-population model selection indicates that capture probabilities varied among occasions (model Mt); however, the closure assumption is questionable due to potential inshore-offshore movement. Therefore, I am also considering POPAN models. There is no evidence of substantial lack of fit of the global POPAN model Phi(t) p(t) pent(t). Models assuming constant Phi or pent seem reasonable because intervals between occasions are fairly consistent and the data are too sparse for the fully time-dependent model to be well supported. In addition to the global model, I am fitting model Phi(.) p(t) pent(.), a death-only model Phi(.) p(t) pent(0), a birth-only model Phi(1) p(t) pent(.), and a closed model Phi(1) p(t) pent(0). I specify constant pent by modifying the design matrix as explained in the MARK book and as I have done successfully with other data sets. The global model runs with no apparent problems. However, when I run model Phi(.) p(t) pent(.) with the default 2ndPart variance estimation, I receive the following message:

* * WARNING * * Divide by zero occurred during variance-covariance calculation of this model.
IEEE flag status at end of variance-covariance calculation:
overflow F
divide by zero T
invalid T
underflow F
inexact T

I have fitted models to comparable data sets for various lakes and years, and this result occurs consistently. Estimated Phi and pent are usually near 1 and 0, respectively, so I wonder if this has something to do with it. I don't receive this message when I run the death-only, birth-only, or closed POPAN models, and the parameter estimates from those models look good. The Phi(.) p(t) pent(.) model runs without error messages if I use the Hessian variance estimation, but then the variance appears to be underestimated. I have searched the MARK book, POPAN literature, and this forum and cannot figure out what's wrong. Am I missing something obvious? Thanks.
stshroye
 
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Re: POPAN divide by zero error message

Postby stshroye » Thu Jul 07, 2022 4:24 pm

I still have not found a definitive explanation for the error message, but after continuing to struggle with it I am beginning to think it means my data are too sparse for the model to work. Does anyone know if this is correct? Thanks.
stshroye
 
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Re: POPAN divide by zero error message

Postby cooch » Thu Jul 07, 2022 4:32 pm

stshroye wrote:I still have not found a definitive explanation for the error message, but after continuing to struggle with it I am beginning to think it means my data are too sparse for the model to work. Does anyone know if this is correct? Thanks.


More than likely...data requirements go up as a function of the number of structural parameters in the model.
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Re: POPAN divide by zero error message

Postby stshroye » Fri Jul 08, 2022 10:13 am

I had read and re-read Schwarz and Arnason (1996), but somehow overlooked the answer:

"Problems usually arise with identifiability issues if {p} are allowed to vary
over time. They can also arise in sparse data, e.g., if z(i)=0, then some parameters are no
longer identifiable.
"

I have some z(i) = 0.
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