--- On Thu, 4/2/10, Mike Smith wrote:
> I am trying to do propensity score matching, but first need
> to do logistic regression and that's what I am have trouble
> with. suppose I have a model as follows: gpa (the dependent
> variable) and sex and race being the independent variables.
<snip>
This suggests that you think you can make propensity weights
by estimating a logit on a continuous variable. logistic
regression is a model for a binary depedent variable, so this
way you make propensity scores when your treatment variable
is binary. Estimating a causal effects for continous
explanatory variables is much harder. See for instance Stephen
L. Morgan and Christopher Winship (2007) Counterfactuals and
Causal Inference: Methods and Principles for Social Research.
Cambridge University Press. I am not recomending that you
turn gpa in a binary variable, in most cases that just doesn't
make substantive sense. The book I refered to earlier does
provide some options for continous explanatory variables.
Hope this helps,
Maarten
--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany
http://www.maartenbuis.nl
--------------------------
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