The Newcastle–Ottawa Scale for Assessing the Quality of Studies in Systematic Reviews

Secondary research is a cornerstone of health sciences, with substantial implications for clinical practice and health policy. Within the systematic review process, a key step is assessing study quality and risk of bias. Among the tools available for evaluating observational studies, the Newcastle–Ottawa Scale (NOS) holds a prominent position and is widely applied in medical research. However, ambiguities and excessive subjectivity have been noted in its application. In this commentary, we discuss the Newcastle–Ottawa Scale guidelines, providing illustrative examples and practical recommendations for completing its items. Improving the accuracy of risk-of-bias assessment is crucial for enhancing the reliability of data synthesis and interpretation in the health sciences.