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st: how can I compute a risk difference with a confidence interval from a logistic model with a categorical*continous interaction?l


From   Eva Katz <ekatz@unc.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: how can I compute a risk difference with a confidence interval from a logistic model with a categorical*continous interaction?l
Date   Tue, 18 Aug 2009 16:06:38 -0400


I've been using prvalue command in stata to compute risk difference (RD) estimates with confidence intervals from a logistic model (citation: Confidence Intervals for Predicted Outcomes in Regression Models for Categorical Outcomes Jun Xu and J. Scott Long Indiana University August 23, 2005). I have a model with an interaction term (dichotomous x continuous variable) and I would like to compute the RD for each level of the continuous variable - compared to a referent value - within each level of the dichotomous variable. For example, my continuous variable is BMI and my categorical variable is a genetic factor (present/absent) I want to know the RD associated with each level of BMI (compared to the referent BMI of 21) among individuals with the genetic factor and among individuals without the genetic factor. However, I do not know how to get a CI when the genetic factor is present.
How do I do this?

thanks!
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