Identifying the 'incredible'! Part 2: Spot the difference-a rigorous risk of bias assessment can alter the main findings of a systematic review

Abstract

The biomedical literature expands by 22 systematic reviews daily,9 with no evidence that production is waning. More systematic reviews are desirable if they identify and inform important research questions that improve patient care.10 However, production of this magnitude is problematic when systematic reviews offer ‘extensive redundancy, little value, misleading claims and/or vested interests’.11 As we outlined in part 1, bias is a systematic deviation from the truth in the results of a research study due to limitations in study design, conduct, or analysis.2 Deviations may either overestimate or underestimate a study’s true findings depending of the type and magnitude of bias. As the results of a systematic review are only as valid as the studies it includes, pooling biased results from different studies can compromise the credibility of systematic review findings when no assessment, or a poor assessment, of risk of bias is performed.3 12