You could also check out the following papers:
@ARTICLE{Stefansson96,
author = "Gunnar Stef\'{a}nsson",
title = "Analysis of groundfish survey abundance data: combining
the GLM and delta approaches",
journal = "ICES Journal of Marine Science",
year = "1996",
volume = "53",
pages = "577--588"
}
@ARTICLE{Waiwoodetal91,
author = "K. G. Waiwood and S. J. Smith and M. R. Petersen",
title = "{Feeding of cod ({\it Gadus morhua}) at low temperatures}",
journal = "Canadian Journal of Fisheries and Aquatic Science",
year = "1991",
volume = "48",
pages = "824--831"
Stephen Smith
-----Original Message-----
From: Andrew Robinson [mailto:andrewr@uidaho.edu]
Sent: March 26, 2004 1:44 PM
To: jadhavpr@vcu.edu; s-news@wubios.wustl.edu; Bill Shipley
Subject: [S] hurdle or two-step models
Off-list requests have suggested that more details might be useful.
The hurdle or two-step models are based on the following approach:
Step 1 (the hurdle): divide the response variable into two classes: 0 and
non-zero. Predict the probability of 0 using a glm or glmm.
Step 2: analyze only the non-zero data using whatever model is appropriate
opr
necessary.
See e.g. Ferguson, D. E., A. R. Stage, and R. J. Boyd. 1986. Predicting
regeneration in the grand fir-cedar-hemlock ecosystem of the northern Rocky
Mountains. Forest Science Monograph 1986, No 26.
Other tools, such as ZIP (zero-inflated Poisson) etc. might also be
appropriate.
Andrew.
--
Andrew Robinson Ph: 208 885 7115
Department of Forest Resources Fa: 208 885 6226
University of Idaho E : andrewr@uidaho.edu
PO Box 441133 W : http://www.uidaho.edu/~andrewr
Moscow ID 83843 Or: http://www.biometrics.uidaho.edu
No statement above necessarily represents my employer's opinion.
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