[R] Zero-inflated regression models: predicting no 0s

[Michael Dewey]

At 18:10 02/06/2011, geojs wrote:
>Thanks for the quick reply,
>
>I understand that the predict(zip1A, type = "response") command is computing
>the fitted_means and these are different than the probabilities
>predict(zip1A, type = "prob"). Although, according to Martin (2005), the
>highest probabilities do not simply lead to the true count estimates: "to
>get the true estimate of relative mean abundance from the ZIP one must
>multiply the estimated relative mean number of individuals at a site by the
>probability that the relative mean number of individuals at a site is
>generated through a Poisson distribution."
>
>I initially thought that the predicted mean and the observed count could be
>compared to estimate the fit of the model, but now I am not sure what to
>think with Martin (2005) statement.

When I started using zero-inflated models I found 
the vignette enormously helpful not only in 
understanding the models but also in teaching a 
few R programming ideas which I have used 
repeatedly since. I am sure Z is too modest to 
say this but it really will repay serious study.


>Thank you for your help,
>
>JM
>
>Martin, T.G. et al. (2005) Zero tolerance ecology: improving ecological
>inference by modelling the source of zero observations, Ecology Letters,
>Volume 8, Issue 11, pages 1235­1246.
>
>--
>View this message in context: 
>http://r.789695.n4.nabble.com/Zero-inflated-regression-models-predicting-no-0s-tp3564807p3568865.html
>Sent from the R help mailing list archive at Nabble.com.

Michael Dewey
info at aghmed.fsnet.co.uk
http://www.aghmed.fsnet.co.uk/home.html