Assessing the quality of studies in meta-analyses: Advantages and limitations of the Newcastle Ottawa Scale

One of the most important points in the meta-analyses is certainly represented by the assessment of the quality of the studies included in such research. The meta-analyses are considered the highest level of evidence in science. Also for this reason, the quality of the studies included should be accurately evaluated by standardized tools. The overall results of the meta-analysis depend indeed also on a rigorous evaluation of the studies quality. Among all the possible tools for this complex evaluation, the Newcastle Ottawa Scale (NOS) is one of the most used worldwide, above all for observational studies. In this review, we will discuss the strengths and limitation of the NOS, also on the basis of the branch of science in which it has been applied.