Volume 48 | Number 3 | June 2013

Abstract List

Marco D. Huesch


Assessing the real‐world comparative effectiveness of common interventions is challenged by unmeasured confounding.


To determine whether the mortality benefit shown for drug‐eluting stents () over bare metal stents () in observational studies persists after controls for/tests for confounding.

Data Sources/Study Setting

Retrospective observational study involving 38,019 patients, 65 years or older admitted for an index percutaneous coronary intervention receiving or in ennsylvania in 2004–2005 followed up for death through 3 years.

Study Design

Analysis was at the patient level. Mortality was analyzed with ox proportional hazards models allowing for stratification by disease severity or use propensity, accounting for clustering of patients. Instrumental variables analysis used lagged physician stent usage to proxy for the focal stent type decision. A method originating in work by ornfield and others in 1954 and popularized by reenland in 1996 was used to assess robustness to confounding.

Principal Findings

was associated with a significantly lower adjusted risk of death at 3 years in ox and in instrumented analyses. An implausibly strong hypothetical unobserved confounder would be required to fully explain these results.


Confounding by indication can bias observational studies. No strong evidence of such selection biases was found in the reduced risk of death among elderly patients receiving instead of in a ennsylvanian state‐wide population.