Article
Diagnosing and responding to violations in the positivity assumption.
Statistical methods in medical research - 1 Feb 2012
Petersen Maya L, Porter Kristin E, Gruber Susan, Wang Yue, van der Laan Mark J
Abstract excerpt
The assumption of positivity or experimental treatment assignment requires that observed treatment levels vary within confounder strata. This article discusses the positivity assumption in the context of assessing model and parameter-specific identifiability of causal effects. Positivity violations occur when certain subgroups in a sample rarely or never receive some treatments of interest. The resulting sparsity...
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