This document discusses assessing risk of bias in studies included in systematic reviews. It defines bias as systematic error that can vary in direction and magnitude. The Cochrane Risk of Bias tool is recommended for assessing bias in domains such as selection bias, performance bias, detection bias, attrition bias, and reporting bias. Assessments involve describing the risk of bias and making a judgment of low, high, or unclear risk. Summary assessments of risk of bias are made within and across studies.

13. Risk of Bias tool (continued) Examples of descriptions

22. Allocation concealment vs. blinding time randomisation Concealment of allocation Blinding Selection bias Performance bias

38. Risk of bias in RevMan 5 RoB for each study

41. RoB in RevMan 5 – a closer look ‡ ‡ Entries depend on item, whether at study or outcome level

42. Example Risk of Bias table

43. RoB optional figure (RevMan 5)

44. RoB optional figure (RevMan 5)

47. Possible approach Most information is from studies at low risk of bias Low risk of bias for all key domains Plausible bias unlikely to seriously alter the results Low Across studies Within a study Interpretation Risk of bias

48. Possible approach (continued) Most information is form studies at low or unclear risk of bias Unclear risk of bias for one or more key domains Plausible bias that raises some doubts about the results Unclear Across studies Within a study Interpretation Risk of bias

49. Possible approach (continued) The proportion of information from studies at high risk of bias is sufficient to affect the interpretation of the results High risk of bias for one or more key domains Plausible bias that seriously weakens confidence in the results High Across studies Within a study Interpretation Risk of bias

51. Reporting biases (continued)

52. Risk of bias exercise