From 1991 to 2015, MEDLINE®, Pubmed central, Embase and Cochrane Library were searched. 
MEDLINE
From 1991 to 2015, MEDLINE®, Pubmed central, Embase and Cochrane Library were searched. 
Pubmed central
From 1991 to 2015, MEDLINE®, Pubmed central, Embase and Cochrane Library were searched. 
Embase
From 1991 to 2015, MEDLINE®, Pubmed central, Embase and Cochrane Library were searched. 
Cochrane Library