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st: Question about correlated variables in zinb regression
From
rachel grant <[email protected]>
To
[email protected]
Subject
st: Question about correlated variables in zinb regression
Date
Fri, 11 Mar 2011 16:01:52 +0000
dear Stata list
I am modelling counts of amphibians arriving at a breeding site with
zinb regression. I am using two variables to predict zeros, DEGD and
TMIN. These two are highly correlated with each other (0.8 correlation
coefficient) as one is derived partially from the other. if I run the
model with one or other of the variables, then I get a significant
negative correlation with zeros, which is what I would expect. But if
I include them both in the model one coefficent is negative and one
becomes positive! it is not really possible that there can be a
positive correlation between this variable and my zero counts, it
makes no sense. Can anyone shed light on this, many thanks
--
regards, Rachel Grant
Dept. Life Sciences
Open University
UK
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