including knowledge about sex that changes during sampling

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including knowledge about sex that changes during sampling

Postby Lyndon » Tue Nov 15, 2016 11:17 pm

I remember a discussion that went something like this: . "If you discover the sex of an individual through the course of a study, you should not go back and adjust the sex status of the individual for the occasions prior to that discovery; you should use a multistate model and model this as a change of state at the time of the discovery."
Does anyone have thoughts about this?
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Re: including knowledge about sex that changes during sampli

Postby simone77 » Sun Feb 19, 2017 11:59 am

This answer comes very late - sorry for not seeing it before - anyway it might be helpful to someone dealing with a similar problem.
This is the kind of issues that multi-event models handle very easy and well.
You may define 3 states (Fem_Alive, Mal_Alive, Dead), 4 events (0= not capt, 1= capt as female, 2= capt as male, 3= capt as unknown sex) and, if you have some individuals whose sex is known from the very first time they are captured, 3 groups (females at 1st capt, males at 1st capt, unknown at 1st capt). Groups may help to get better precision because they provide a kind of ancillary information (more on this below).

Then, in GEPAT, that is where you define the probability matrices, you set something like this

If you have been able to define the groups you may use a sentence like this in GEMACO for the Initial State: "" which is telling ESURGE to estimate an Initial State probability (in this case p of being male when first captured) for each group. Then, in IVFV, that's where you are allowed to fix parameters to a certain value, you fix g(1) (i.e. females) to 0, g(2) (i.e. males) to 1 and let it calculating the initial state probability of being male for the g(3).

You may have several different situations similar to this that is where ESURGE gives you a plus to modeling CMR data.

A good and illustrative paper to be read for that is:
Genovart, M., Pradel, R., & Oro, D. (2012). Exploiting uncertain ecological fieldwork data with multi‐event capture–recapture modelling: an example with bird sex assignment. Journal of animal ecology, 81(5), 970-977.
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