[R-sig-ME] (no subject)

[Nicholas Lewin-Koh]

Hi Thierry,
The other responses you've gotten all address your question. I was
wondering
if you had considered coverage estimators? These are used to address
problems
of census undercount, which seems to be the issue here. Anne Chao has
written
a great deal on this, and there is a vast literature on estimating the
number
of species in a community which uses similar models. Just a thought.

Nicholas

> Date: Thu, 28 Jan 2010 11:12:44 +0100
> From: "ONKELINX, Thierry" <Thierry.ONKELINX at inbo.be>
> To: <r-sig-mixed-models at r-project.org>
> Subject: [R-sig-ME] Trend in total number of animals
> Message-ID:
> 	<2E9C414912813E4EB981326983E0A10406F91914 at inboexch.inbo.be>
> Content-Type: text/plain
> 
> Dear all,
>  
> We are modelling the total numbers of hibarnating bats in a fortress. We
> have data of the number of bats per room spanning ten years. The main
> problem is that not all rooms were visited each year. The fieldworkers
> did not known or find all rooms and some rooms were not allways
> accessible.
>  
> Some of the rooms were not counted in the early years and they contain a
> rather high number of bats in the more recent years. So a glm on the
> total observed number would be very biased. Therefore we would use a
> mixed model on the numbers of bats per room. The model looks like:
> glmer(Number ~ Year + (1|Year) + (Year|Room), family = poisson). Year is
> the long-term trend. (1|Year) allows for year-to-year variability (due
> to weatherconditions) and (Year|Room) allows for a random intercept and
> slope per room.
>  
> Our main question about this model is the interpretation of the
> long-term trend (fixed effect of Year). Given the model specification it
> is the trend in an 'average' room from the population of rooms. Can we
> assume that this trend equals the trend in the total number of bats in
> the fortress. That would be the trend in to total observed numbers if we
> could have investigated every room in every year.
> Or is it better to use the model to simulate the total number of bats
> and then model this simulated totals using a simple glm? Repeating the
> simulations a large number of times would yield an average and
> confidence intervals for the trend.
>  
> Best regards,
>  
> Thierry
> 
> ------------------------------------------------------------------------
> ----
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek
> team Biometrie & Kwaliteitszorg
> Gaverstraat 4
> 9500 Geraardsbergen
> Belgium
> 
> Research Institute for Nature and Forest
> team Biometrics & Quality Assurance
> Gaverstraat 4
> 9500 Geraardsbergen
> Belgium
> 
> tel. + 32 54/436 185
> Thierry.Onkelinx at inbo.be
> www.inbo.be
> 
> To call in the statistician after the experiment is done may be no more
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> ~ Roger Brinner
> 
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> data.
> ~ John Tukey
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> End of R-sig-mixed-models Digest, Vol 37, Issue 19
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