JACC Cardiovasc Interv. 2008 Jun;1(3):211-7

Hannan EL. SUNY University at Albany, School of Public Health, Rensselaer, New York 12144-3456, USA

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