Table 1

Differences between the original risk of bias tool and RoB2 for assessing randomised controlled trials

Original risk of bias toolRoB 2
Focus of assessmentOutcome level, for example, subjective and objective outcomes should be assessed separately (however, in practice, this tool has often been used at the study level)Result level, such that a numerical result is specified as the focus of the assessment (if there is no numerical result for an outcome from a specific study, then there is no need to complete a risk of bias assessment as it will not be contributing to the review)
StructureSeven recommended bias domains, with the option of adding or deleting domains
Risk of bias judgement for each domain only
Preliminary considerations
Five fixed bias domains
Signalling questions
Risk of bias judgement for each domain and overall
  • Random sequence generation (‘selection bias’)

  • Allocation concealment (‘selection bias’)

  • Blinding of participants and personnel (‘performance bias’)

  • Blinding of outcome assessment (‘detection bias’)

  • Incomplete outcome data (‘ttrition bias’)

  • Selective reporting (‘reporting bias’)*

  • Other bias†

  • Bias arising from the randomisation process

  • Bias due to deviations from intended interventions

  • Bias due to missing outcome data

  • Bias in measurement of the outcome

  • Bias in selection of the reported result

Plus ‘Overall risk of bias’
Basis of judgementAuthor derivedSignalling questions answered yes; probably yes; probably no; no; no information with suggested algorithm for reaching judgement
Judgement optionsLow risk—unclear—high riskLow risk—some concerns—high risk (plus optional direction of bias)
  • Guidance for using the original risk of bias tool is available in V.5.2 of the Cochrane Handbook.

  • *As RoB 2 assesses risk of bias in a numerical result, risk of bias due to missing results (from non-publication of trials or results) is not part of the revised tool. This can be assessed using the Risk of Bias-Missing Evidence; available on the Risk of Bias tools website (

  • †RoB 2 does not include an ‘other bias’ domain. All domains within RoB 2 include trial features that directly influence the risk of bias; those that indirectly influence the risk of bias should be assessed in other stages of the review, or example,for conflicts of interest a Tool for Addressing Conflicts of Interest in Trials is in development.16

  • RoB2, Risk of Bias 2.