Previous studies associating the use of proton pump inhibitors (PPI) — which include popular anti-heartburn medications like Prilosec and Nexium — with an increased incidence of pneumonia may not have found a true cause-and-effect relationship. A new study outlines a strategy for determining when the results of such observational studies may have been distorted by unmeasured factors and then finds that may be the case with the association between PPIs and pneumonia risk.