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...ette containing some basic theory and walks through two examples. It is available by typing vignette("twang") at the R prompt after loading the library. Background on the methodology with an application to evaluating drug treatment programs is available in McCaffrey, D., G. Ridgeway, A. Morral (2004). "Propensity score estimation with boosted regression for evaluating adolescent substance abuse treatment," Psychological Methods 9(4):403-425. -------------------- This email message is for the sole use of the intended recip...{{dropped}} ______________________________________...

Dear List, I am having difficulty running the ps() function when variables are stored as factors and was hoping someone could provide some advice on how to proceed. I am running propensity score matching as outlined in: Greg Ridgeway, Dan McCarey, Andrew Morral, Lane Burgette and Beth Ann Grin (May 3, 2013) Toolkit for Weighting and Analysis of Nonequivalent Groups: A tutorial for the twang package and have a question about using unordered categorical variables as a covariates. The tutorial indicates that: "There is no need to ? create indicator,...

...part of this is the development of a propensity score model (when the exposure is binary). I would like to use tools/approaches that can do this semi-automatically so that the resulting model has both low prediction error and good covariate balance. I have read your paper (McCaffrey, Ridgeway and Morral 2004), which uses a gradient boosting machine (gbm) to build a logistic regression model for propensity score. I was wondering whether there are other tools that can also address this problem, for example, glmpath or MARS? An important question is whether these "machine learning" metho...