Fixing Parameters to 1 for Known-fate Models

questions concerning analysis/theory using program MARK

Fixing Parameters to 1 for Known-fate Models

Postby tracker » Thu Jan 11, 2018 1:53 pm

I am rather new to MARK, and I was wondering if for Known-fate models it is appropriate to fix parameters to 1 in time-dependent models for time intervals where no mortalities are known to have occurred?

It is my understanding from section 16.4 of the MARK Gentle Introduction book and the worked black duck example that the number of model parameters estimated when using the design matrix and logit function should be readjusted to include those parameters where survival was estimated at 1. However, some journal articles that have used Known-fate models have described in their methods that they fixed parameters to 1 when no mortalities were known to have occurred in an interval (e.g. Jones et al. 2012, "Range‐wide analysis of eastern massasauga survivorship"). Which method is the "correct" way to go about accounting for such intervals in time-dependent KF models in MARK?

Any advice at all would be much appreciated, and thank you for your time!
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Re: Fixing Parameters to 1 for Known-fate Models

Postby Bill Kendall » Thu Jan 11, 2018 3:37 pm

For known fate (a simple binomial model without the need to estimate detection probability), when all individuals survive the interval you should always get an estimated survival of 1.0, whether or not you fix the value. And whether you fix it or not, you should still include it in the number of estimated parameters, because the data are there to estimate it (although because it is on the boundary MARK will not count include it in the parameter count).
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Re: Fixing Parameters to 1 for Known-fate Models

Postby tracker » Thu Jan 11, 2018 3:50 pm

Ah, okay, good to know. Thank you!
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