Predicted values for zero-inflated Poisson

Hi all-

I fit a zero-inflated Poisson model to model bycatch rates using an offset
term for effort. I need to apply the fitted model to a datasets of varying
levels of effort to predict the associated levels of bycatch. I am seeking
assistance as to the correct way to code this.


---
Just use the function zeroinfl from the pscl package...fit your
model...extract the estimated parameters, specify a data frame with
variables for which you want to make predictions (including values for
your offset), use model.matrix to convert it into the correct format and
calculate your fitted values.

You can also use the function predict.

You can either predict the binary (pi) and count parts (mu), or the
predicted values for the ZIP ((1-pi)*mu)..or better...both. 


For detailed examples and code see: 

Zero Inflated Models and Generalized Linear Mixed Models with R. (2012) 
Zuur, Saveliev, Ieno.

http://www.highstat.com/book4.htm


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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Highland Statistics Ltd.
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UK - AB41 6FN Newburgh
Tel: 0044 1358 788177
Email: highstat at highstat.com
URL: www.highstat.com
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Thanks in advance!

Laura





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