Electronic searches of Medline, PubMed, and the Cochrane Database of Systematic Reviews since inception to September 2013 were conducted to identify all relevant studies. 
Medline
Electronic searches of Medline, PubMed, and the Cochrane Database of Systematic Reviews since inception to September 2013 were conducted to identify all relevant studies. 
PubMed
Electronic searches of Medline, PubMed, and the Cochrane Database of Systematic Reviews since inception to September 2013 were conducted to identify all relevant studies. 
Cochrane Database of Systematic Reviews