Search and selection
The final electronic search identified 1214 database articles, 337 from Cochrane Library, 389 from PubMed, 214 from EMbase, 114 from Web of Science and 160 from SpringerLink. After removal of duplicates, 956 records remained, from which 905 were excluded through screening on the basis of titles and abstracts. And the remained 51 articles were read in full. Forty publications were further excluded as they did not meet inclusion criteria or lack of available data, leaving 11 as eligible studies for this systematic review. Details of the selection process are presented in Fig. Flow chart of study selection process according to PRISMA diagram