2.4 Quality Assessment and Sensitivity Analysis
The Newcastle–Ottawa scale was applied to evaluate the quality of the included studies and their risk of bias, and all of them had Newcastle–Ottawa scores between 7 and 8, which ensured that they all had high quality. We also performed sensitivity analyses to assess the robustness of the findings and investigated the heterogeneity of the included studies, assessing the impact of each study on the pooled results and treating a study as a causation of high heterogeneity if it was excluded because of its significantly lower I2.