This is an archived version of the Handbook. For the current version, please go to or search for this chapter here.

8.5.3  The judgement

Review authors’ judgements should be categorized as ‘Low risk’ of bias, ‘High risk’ of bias or ‘Unclear risk’ of bias. The assessments should consider the risk of material bias rather than any bias. We define ‘material bias’ as bias of sufficient magnitude to have a notable impact on the results or conclusions of the trial, recognizing that subjectivity is involved in any such judgement.


Table 8.5.d provides criteria for making judgements about risk of bias from each of the seven domains in the tool. If insufficient detail is reported of what happened in the study, the judgement will usually be ‘Unclear risk’ of bias. An ‘Unclear’ judgement should also be made if what happened in the study is known, but the risk of bias is unknown; or if an entry is not relevant to the study at hand (particularly for assessing blinding and incomplete outcome data, when the outcome being assessed by the entry has not been measured in the study).