Hello,

I am looking to generate propensity score in R using ps() command. My
question comes from how to include categorical variables in the equation to
generate propensity score. How should I include reference category in the
estimation? Should I drop the reference group manually before running the
estimation or R would automatically omit it as if I include it in the
estimation? I look forward to your response!

Qian Zhang
Department of Sociology
University of South Carolina

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