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8.7  Summary assessments of risk of bias

The Collaboration’s recommended tool for assessing risk of bias in included studies involves the assessment and presentation of individual domains, such as allocation concealment and blinding. To draw conclusions about the overall risk of bias for an outcome it is necessary to summarize these. The use of scales (in which scores for multiple items are added up to produce a total) is discouraged for reasons outlined in Section 8.3.1.


Nonetheless, any assessment of the overall risk of bias involves consideration of the relative importance of different domains. A review author will have to make judgements about which domains are most important in the current review. For example, for highly subjective outcomes such as pain, authors may decide that blinding of participants is critical. How such judgements are reached should be made explicit and they should be informed by:


Summary assessment of risk of bias might be considered at four levels:


Review authors should make explicit judgements about the risk of bias for important outcomes both within and across studies. This requires identifying the most important domains (‘key domains’) that feed into these summary assessments. Table 8.7.a provides a possible approach to making summary assessments of the risk of bias for important outcomes within and across studies.