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Randomized Clinical Trials and Observational Studies

Guidelines for Assessing Respective Strengths and Limitations

University at Albany School of Public Health, Rensselaer, New York.

^_* Reprint requests and correspondence: Dr. Edward L. Hannan, School of Public Health, State University of New York, Department of Health Policy, Management and Behavior, SUNY University at Albany, One University Place, Rensselaer, New York 12144-3456. (Email: elh03{at}health.state.ny.us).

The 2 primary types of studies that are used to test new drugs or procedures or compare competing drugs or types of procedures are randomized clinical trials (RCTs) and observational studies (OS). Although it would appear that RCTs always trump OS because they eliminate selection bias, there are many possible limitations to both types of studies, and these limitations must be carefully assessed when comparing the results of RCTs and OS. This state-of-the art review describes these limitations and discusses how to assess the validity of RCTs and OS that yield different conclusions regarding the relative merit of competing treatments/interventions.

Abbreviations and Acronyms   BMS = bare-metal stent(s)   CABG = coronary artery bypass graft   CI = confidence interval   DES = drug-eluting stent(s)   HRT = hormone replacement therapy   OR = odds ratio   OS = observational study/studies   PES = paclitaxel-eluting stent(s)   PTCA = percutaneous translumincal coronary angioplasty   RCT = randomized controlled trial(s)   RR = relative risk