2.7.1. Subgroup analysis and sensitivity analysis

If the heterogeneity is large, we will conduct a subgroup analysis of age, duration of treatment, course of VD and study quality to find the source of heterogeneity. We will conduct sensitivity analysis of outcome indicators and exclude references article by article. If the heterogeneity changes after excluding a certain reference, it indicates that the reference may be the source of heterogeneity. In addition, the reasons for heterogeneity can be explained by analyzing sample size, experimental design, outcome indicators, evaluation criteria, etc. If the heterogeneity remains unchanged after the exclusion of literature article by article, the results are relatively robust.