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

geojs michaud2 at interchange.ubc.ca
Thu Jun 2 19:10:53 CEST 2011


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. 

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 1235–1246.


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