Beginner's Question - Capture probability & Assumptions

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Beginner's Question - Capture probability & Assumptions

Postby smw62 » Mon Jan 22, 2018 12:46 pm

Hi,
This is a very basic question that I hope someone can answer with one word.
From the literature: Most crucial assumption is capture probability remains homogenous over the study.

My best fitting open population model (POPAN) uses a time dependence estimate for capture probability.

Does using this model violate the assumption?

I am trying to get a population estimate of eels passing through a barrier. There are no environmental (short study), behavioural (no avoidance), or biological factors (all young females) that would skew individual capture probabilities, before or after tagging. So I thought the capture probability would remain the same for all individuals.
Does the time dependence apply to the entire population? I.e. the capture probabilities remain homogenous for individuals across the study, but at each sampling point it can change so it doesn't actually violate the assumption?
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Re: Beginner's Question - Capture probability & Assumptions

Postby Bryan Hamilton » Mon Jan 22, 2018 2:09 pm

No the time dependent model does not violate the assumption of homogenous capture probabilities.

It allows varying capture probabilities by time period, but within time periods, capture probabilities are homogenous across individuals.
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Re: Beginner's Question - Capture probability & Assumptions

Postby smw62 » Mon Jan 22, 2018 3:16 pm

Awesome, thanks so much
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Re: Beginner's Question - Capture probability & Assumptions

Postby murray.efford » Mon Jan 22, 2018 4:49 pm

Taking this a little further... The assumption is that there is no unmodelled variation in capture probability. Hence the industry supplying models for capture probability, of which the time-dependent model is one example. Rather than representing a violation of the assumption, it increases the chance of compliance.
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