3.1. Study selection
A total of 364 relevant documents were retrieved by the search methods above, including 103 articles from PubMed, 96 articles from Web of Science, 66 articles from EMBASE, and 99 articles from MEDLINE. We hand-searched bibliographies of retrieved papers and 2 article was included. After removing 248 duplicate documents, 82 papers were deemed ineligible after title and abstract screening, and 22 papers were excluded after further screening through full-text reading. After the exclusion of all the 352 unqualified studies, a total of 14 retrospective case analyses were included in this meta-analysis(10-23). The process of study selection is illustrated in Appendix S1.