Initial occupancy, data collection starts in different years

questions concerning analysis/theory using program PRESENCE

Initial occupancy, data collection starts in different years

Postby rasrage » Fri Jul 24, 2015 12:08 pm

Dear all,
I am starting to work on a multi-state multi-season occupancy model. We are looking at multiple study sites, and data collection at the different sites commenced in different years. My question: do the initial occupancy parameters refer to (a) the first year of the study across all site, sampled or not, and occupancy is predicted for those sites not sampled in the first year; or (b) to the first year each site was sampled (so that could be year 1 for some sites, year 2 for others, and so forth)?
It feels like a very basic question but I haven't been able to find an answer in the existing documentation. Apologies if I overlooked something.
Thank you!
Rahel
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Re: Initial occupancy, data collection starts in different y

Postby jhines » Fri Jul 24, 2015 12:51 pm

Initial occupancy refers to the 1st year of data, sampled or not.

Are you saying that study site is the 'state' variable in a multi-state model and some states aren't possible in the 1st year? In the multi-state model, all states have to be sampled each survey or you'll have part of the population which is un-observable.
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Re: Initial occupancy, data collection starts in different y

Postby rasrage » Fri Jul 24, 2015 2:01 pm

Hi Jim,
sorry I wasn't clear. No, 'site' is not the state, it's breeding/non-breeding. So all states are always surveyed. But we're looking at data from a large landscape and while some chunks of the landscape were sampled starting in 2002, others didn't start til several years later. So initial occupancy for these different chunks in the landscape would refer to different years, if it referred to the first year an area was surveyed. Does that make sense?
Thanks!
Rahel
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Re: Initial occupancy, data collection starts in different y

Postby rasrage » Fri Jul 24, 2015 3:35 pm

Jim, just saw the first sentence of your previous reply, which is exactly the answer I was looking for! Thanks so much!
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Re: Initial occupancy, data collection starts in different y

Postby Eurycea » Fri Jul 24, 2015 3:39 pm

If you are coding missing values for 2002 for sites that were not surveyed until later, then your initial occupancy will be for 2002. If you are "shifting" all your data in time, so the start of surveys lines up say, 2002 and 2004 are in the same row of data, then your initial occupancy will be for that first year. If you are doing the latter, it seems like it would preclude the use of any models with time variation.

Nate
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