To the Editor: Dr Malenka and colleagues1 described the protective effect of drug-eluting stents against repeat revascularization procedures by comparing frequency of revascularization in the bare-metal stent era to the frequency after drug-eluting stents came on the market. In doing so, they took a step back from the exposure itself—drug-eluting vs bare-metal stent—and instead implicitly used the era as a proxy for the stent exposure. Presumably, they did this because they believed that the exposure to drug-eluting stent would be confounded by unmeasured factors that they could not adjust for with the available data.
Rassen JA, Schneeweiss S. Outcomes in the Era of Bare-Metal Stents vs the Era of Drug-Eluting Stents. JAMA. 2009;301(1):33-34. doi:10.1001/jama.2008.899