RT Journal Article SR Electronic T1 Tips for learners of evidence-based medicine: 4. Assessing heterogeneity of primary studies in systematic reviews and whether to combine their results JF Canadian Medical Association Journal JO CMAJ FD Canadian Medical Association SP 661 OP 665 DO 10.1503/cmaj.1031920 VO 172 IS 5 A1 Rose Hatala A1 Sheri Keitz A1 Peter Wyer A1 Gordon Guyatt A1 for The Evidence-Based Medicine Teaching Tips Working Group YR 2005 UL http://www.cmaj.ca/content/172/5/661.abstract