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From | Adam Olszewski <adam.olszewski@gmail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: Treatment by propensity score interaction |
Date | Mon, 8 Apr 2013 22:31:26 -0400 |
Hi Perry, This is a very interesting question and is currently a subject of research. It has a lot to do with the "subset analyses" and "heterogeneity of treatment effect" issue that comes up in the randomized trials. It may indeed uncover unobserved confounding, although not necessarily - it might just indicate heterogeneous treatment effect (i.e. patients at high-end of propensity score may just benefit from the treatment more). Here are two interesting articles that have dealt with this problem: Lunt M, Solomon D, Rothman K, et al. Different methods of balancing covariates leading to different effect estimates in the presence of effect modification. Am J Epidemiol. 2009;169(7):909-917. (they propose the interaction test as a sensitivity analysis) Kurth T, Walker AM, Glynn RJ, et al. Results of multivariable logistic regression, propensity matching, propensity adjustment, and propensity-based weighting under conditions of nonuniform effect. Am J Epidemiol. 2006;163(3):262-270. (an extreme example of a failed propensity score analysis in a setting of poor overlap and highly heterogeneous effect) I hope it's a start of an interesting reading direction. Of course there is also a wealth of literature on the interaction testing for treatment heterogeneity in the randomized trials. Adam Olszewski On Mon, Apr 8, 2013 at 9:33 AM, Perry Wilson <fpwilson3@gmail.com> wrote: > Hi Statalisters, > > I have an intuition about a propensity score model and I'm wondering if I'm > out in left field or if there is some literature to support this. > > -I have a treatment X and an outcome of interest Y. > -I estimate the probability of receiving treatment X via a logistic > regression model. > -I can then match on that probability for patients who are treated (X1) and > not treated (X0) and assess the effect of X on Y. > > One question that always arises is unmeasured confounding - are matched > treated / untreated patients similar on non-measured characteristics. > -If there is some large unmeasured confounder, I would suspect it to be > present preferentially at the lower range of propensity score (why, after > all are these treated patients getting treated if their probability of > treatment is so low?). > > Here's where I get a little bit more abstract... > -Therefore, if one detects a strong treatment-by-propensity score > interaction on Y, it suggests the presence of such a confounder > -Conversely, if the treatment-by-propensity interaction is not significant, > that would suggest minimal unmeasured confounding? > > Does this make sense? Any literature to back up such a statement? > > Thanks! > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/faqs/resources/statalist-faq/ > * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/