[R] Predicted values for zero-inflated Poisson

Highland Statistics Ltd
Mon, 09 Jul 2012 21:16:43 -0000

Laura Lee laura.lee at ncdenr.gov
Mon Jul 9 22:51:40 CEST 2012

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Thanks for your reply. I do have a copy of "Zero Inflated Models and
Generalized Linear Mixed Models with R" and have been using that as a
guide.
I applied the predict function (type="count") to the dataset for which
I
built the model to compare the predicted bycatch numbers to the observed to
ensure I was doing things correctly. When I summed over the new predicted
variable, the value is over 500 whereas there were less than 10 observed.
I'd appreciate any advice regarding what I'm doing wrong.

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AFZ:
Laura....no...you don't want to compare the count part of the model with raw
data....you need to compare
the Exp(Y) = (1-pi) * mu with the raw data. Have a look at the Epilogue
chapter....it shows the difference
between mu and (1-pi) * mu.



Alain







--

Dr. Alain F. Zuur
First author of:

1. Analysing Ecological Data (2007).
Zuur, AF, Ieno, EN and Smith, GM. Springer. 680 p.
URL: www.springer.com/0-387-45967-7


2. Mixed effects models and extensions in ecology with R. (2009).
Zuur, AF, Ieno, EN, Walker, N, Saveliev, AA, and Smith, GM. Springer.
http://www.springer.com/life+sci/ecology/book/978-0-387-87457-9


3. A Beginner's Guide to R (2009).
Zuur, AF, Ieno, EN, Meesters, EHWG. Springer
http://www.springer.com/statistics/computational/book/978-0-387-93836-3


4. Zero Inflated Models and Generalized Linear Mixed Models with R. (2012) Zuur,
Saveliev, Ieno.
http://www.highstat.com/book4.htm

Other books: http://www.highstat.com/books.htm


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