Tools for assessing quality and risk of bias by levels of evidence

Tools for assessing methodological quality or risk of bias in randomized controlled trials (RCTs) and non-randomized studies (NRS) were reviewed. The van Tulder scale and Cochrane's assessment of risk of bias are the two most useful methodological quality evaluation tools for RCTs. Cochrane's tool includes sequence generation, allocation of sequence concealment, blinding, incomplete outcome data, selective outcome reporting, and other potential sources of bias. The Cochrane Collaboration Group recommends the Downs and Black instrument and the Newcastle-Ottawa Scale for evaluating the quality of NRS. In conclusion, this study offers useful information to physicians about tools for assessing the quality of evidence in clinical guidelines. Further research is needed to provide an essential core for evidence-based decision making regarding levels and/or grades of recommendations.