## Beginner's Question - Capture probability & Assumptions

Forum for discussion of general questions related to study design and/or analysis of existing data - software neutral.

### Beginner's Question - Capture probability & Assumptions

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?
smw62

Posts: 4
Joined: Mon Oct 02, 2017 9:46 am

### Re: Beginner's Question - Capture probability & Assumptions

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.
Bryan Hamilton

Posts: 111
Joined: Thu Jun 15, 2006 11:36 am
Location: Great Basin National Park

### Re: Beginner's Question - Capture probability & Assumptions

Awesome, thanks so much
smw62

Posts: 4
Joined: Mon Oct 02, 2017 9:46 am

### Re: Beginner's Question - Capture probability & Assumptions

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.
murray.efford

Posts: 537
Joined: Mon Sep 29, 2008 7:11 pm
Location: Dunedin, New Zealand