01664nas a2200253   4500000000100000000000100001008004100002260001200043653002400055653002400079653001100103653002600114653002500140653001500165653002000180100001700200700002100217700002000238245004000258300001200298490000700310520107900317022001401396       2019                            d  c2019-0410aBiomedical Research10aDouble-Blind Method10aHumans10aPeer Review, Research10aPeriodicals as Topic10aPublishing10aresearch report1 aSamir Haffar1 aFateh Bazerbachi1 aM. Hassan Murad00aPeer Review Bias: A Critical Review  a670-6760 v943 aVarious types of bias and confounding have been described in the biomedical literature that can affect a study before, during, or after the intervention has been delivered. The peer review process can also introduce bias. A compelling ethical and moral rationale necessitates improving the peer review process. A double-blind peer review system is supported on equipoise and fair-play principles. Triple- and quadruple-blind systems have also been described but are not commonly used. The open peer review system introduces "Skin in the Game" heuristic principles for both authors and reviewers and has a small favorable effect on the quality of published reports. In this exposition, we present, on the basis of a comprehensive literature search of PubMed from its inception until October 20, 2017, various possible mechanisms by which the peer review process can distort research results, and we discuss the evidence supporting different strategies that may mitigate this bias. It is time to improve the quality, transparency, and accountability of the peer review system.  a1942-5546