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st: Re:
At 09:03 PM 8/25/2008, Sampaio, Marcelo wrote:
Dear all
I am a reserch fellow and I use stata to my analysis. I would like
to know what we should do when in a multiple logistic analysis we
have a output saying that the variable was dropped by estimability
or dropped because it is constant. How can we fix it and how much it
affects the analysis?
Thanks
Marcelo Sampaio
Resech Fellow
As Martin notes, if the variable really is a constant, it can't do
anything for your model. However, if you don't believe it should be
a constant, you might double-check your sample selection procedures
or the cases that are being lost because of missing data. For
example, a dummy variable for gender will wind up being a constant if
your sample has been limited to women. This might occur (without you
realizing it) if, say, one of the variables in your model was a
question asked only of women. Particularly in a large survey data
set with lots of skip patterns, it can be a little tricky sometimes
to keep track of just who exactly was asked the questions.
-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
HOME: (574)289-5227
EMAIL: [email protected]
WWW: http://www.nd.edu/~rwilliam
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