, Volume 28, Issue 7, p 873
Date: 04 Apr 2013

Community-Acquired Pneumonia and Proton Pump Inhibitors

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To the Editors:—I thank Drs. Jena, Sun and Goldman for applying an interesting falsification method to investigate the observed association between PPI use and incident community-acquired pneumonia.1 The authors advocate their method as “an intuitive approach to assessing the likelihood of confounding in observational studies” and as perhaps useful “for validating the causal plausibility of observational studies more generally.” I wish to recast the authors’ analysis in a form better aligned with modern concepts of causal inference, clarifying the underlying intuition and suggesting a suitable role for their method in the process of model-based data analysis.

Jena and colleagues begin with a linear probability model in which, despite multiple adjustments, an association persists between PPI fills and CAP diagnosis. Concerned that residual confounding makes their model incorrectly specified to identify the causal effect of PPI on CAP, the authors undertake an interesting demonstration. F ...