RT Journal Article SR Electronic T1 Interpreting meta-analysis in systematic reviews JF Evidence Based Medicine JO Evid Based Med FD BMJ Publishing Group Ltd SP 67 OP 69 DO 10.1136/ebm.13.3.67 VO 13 IS 3 A1 Rafael Perera A1 Carl Heneghan YR 2008 UL http://ebm.bmj.com/content/13/3/67.abstract AB