3.1 Study selection:
The flowchart represents the search and selection strategy for the study. The initial search resulted total 1361 studies, PubMed (n=65), Cochrane Library (n=276), Google Scholar (n=1000) and articles identified through forward/backward search (n=20). 29 articles were excluded as duplicate and 1270 articles were excluded from title and abstract screening. From remaining articles, 24 articles were excluded due to lacking of mortality data in screening full-text content. A total 38 studies were considered in the systematic review (Figure-1).