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External Adjustment Sensitivity Analysis for Unmeasured Confounding: An Application to Coronary Stent Outcomes, Pennsylvania 2004–2008
Author(s) -
Huesch Marco D.
Publication year - 2013
Publication title -
health services research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.706
H-Index - 121
eISSN - 1475-6773
pISSN - 0017-9124
DOI - 10.1111/1475-6773.12013
Subject(s) - confounding , medicine , propensity score matching , observational study , proportional hazards model , stent , population , selection bias , emergency medicine , demography , environmental health , pathology , sociology
Background Assessing the real‐world comparative effectiveness of common interventions is challenged by unmeasured confounding. Objective To determine whether the mortality benefit shown for drug‐eluting stents ( DES ) over bare metal stents ( BMS ) 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 DES or BMS in P ennsylvania in 2004–2005 followed up for death through 3 years. Study Design Analysis was at the patient level. Mortality was analyzed with C ox proportional hazards models allowing for stratification by disease severity or DES 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 C ornfield and others in 1954 and popularized by G reenland in 1996 was used to assess robustness to confounding. Principal Findings DES was associated with a significantly lower adjusted risk of death at 3 years in C ox and in instrumented analyses. An implausibly strong hypothetical unobserved confounder would be required to fully explain these results. Conclusions 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 DES instead of BMS in a P ennsylvanian state‐wide population.