[R] Not sure how to handle hazard in my survival model

[Rainer M Krug]

Dear Freya


On Thu, Mar 10, 2011 at 12:10 PM, bsaj <bsaj at leeds.ac.uk> wrote:
> Hi R experts :)
>
> I'm trying to carry out a survival model on my data, but I am unsure of
> whether it's appropriate or if I should do something specific in regards to
> hazard.
>
> My data is time to death by predator where I have 8 prey and one predator in
> the setting. This means that two prey can't possibly die at the same time
> and I can't quite get my head around how to include this in the model. I
> have repeats, so I have 15 replicates of the 8 prey one predator setting.
> What I have done so far is include replicate as a random factor in a coxme
> (as it is a different predator each time, so the time of death may vary
> depending on predator), but that doesn't really address the issue of prey
> having to die in a sequential manner. I was thinking I could make the time
> to death the time until first prey eaten for prey one and then the time from
> prey one to prey two the time to death for prey two, but I'm not sure if
> that's appropriate. Also, encounter rates will decrease as there are fewer
> prey available and the predator will become less hungry the more prey it
> eats. All the examples (and examples are the way I learn best) have survival
> analysis based on completely independent deaths such as dying from cancer,
> time to flowering etc where the event could happen at the same time for all
> the individuals.

this sounds to me like a rather complicated scenario to model
analytically. Depending on which question you want to answer, I would
be using a simulation model, in which you can weasily put all the
rules you specified. This model can be deterministic or stochastic,
depending on your requirements.

if you have the simulation model, you can then analyse it numerically.

Hope this helps,

Rainer

>
> Can anyone help me get my head around this or maybe point me to some good
> information in a book or online?
>
> Just realised this sounds a bit gruesome, but the prey are frozen bloodworms
> and the predator a small fish.
>
> Thank you ever so much,
>
> Freya
>
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Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
Biology, UCT), Dipl. Phys. (Germany)

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