RT Journal Article SR Electronic T1 Integration of evidence from multiple meta-analyses: a primer on umbrella reviews, treatment networks and multiple treatments meta-analyses JF Canadian Medical Association Journal JO CMAJ FD Canadian Medical Association SP 488 OP 493 DO 10.1503/cmaj.081086 VO 181 IS 8 A1 John P.A. Ioannidis YR 2009 UL http://www.cmaj.ca/content/181/8/488.abstract