Nonrandomized studies are not always found even when selection criteria for health systems intervention reviews include them: a methodological study

Most EPOC reviews consider nonrandomized studies, but the degree to which they find them varies. As nonrandomized studies are believed to be at higher risk of bias and their inclusion entails a considerable effort, review authors should consider whether the benefits justify the inclusion of these designs. Research should explore whether it is more useful to consider nonrandomized studies in reviews of some intervention types than others.