2.3 Assessment of methodological quality
We used the Newcastle-Ottawa scale (NOS) [20] for assessing the
quality of the included studies in this meta-analysis. Using this scale
system, each included study was judged on three broad perspectives: the
selection of the study groups, the comparability of the groups, and the
ascertainment of outcome of interest. High-quality studies were
identified with a NOS score of five or more. Whereas those with less
than a score of five were considered as low-quality studies.