by cooch » Thu Nov 09, 2017 4:06 pm
The basic point is this -- the canonical estimator for abundance is 'count/detection'. With an open CJS model, there is minimum information for p, so the uncertainty for your estimates of N as 'count/detection' is considerable (to the point where many estimates from open models verge on silly). This is the motivation for the many models for estimating abundance from closed populations. Because N is a constant over the closed samples, you can do a much better job modeling the encounter process, and thus your estimate of 'detection' is much better. And thus, so is your derived estimate of abundance. If all you needed to do to get abundance that you had faith in was take number counted at a sampling occasion and divide by the CJS estimate of p, then life would be much simpler. But, alas, life isn't that simple. Short of strong assumptions (which are often the basis of the classic J-S and POPAN-based open models that generate abundance estimates), I generally look at simple 'count/detection' (as per original post) as an index to abundance, but not much more.