A Revised Tool to Assess Risk of Bias in Randomized Trials (RoB 2) Tools

Sterne, J., Savović, J., Page, M. J., Elbers, R. G., Blencowe, N. S., Boutron, I., et al. (2019). RoB 2: A revised tool for assessing risk of bias in randomised trials. BMJ (Clinical research ed.), 366, l4898. https://doi.org/10.1136/bmj.l4898

Template available Evaluated/validated


This framework can be used to assess the risk of bias in any type of randomized control trial. A template is provided to assess the domains in which bias may be introduced in individual randomized control trials. Templates are also provided to assess randomized parallel-group trials, cluster-randomized parallel-group trials and randomized cross-over trials and other matched designs.

Steps for Using Method/Tool

The RoB 2 guides users through a series of signalling questions for each of the five domains through which bias may be introduced:

  1. Bias arising from the randomization process
  2. Bias due to deviations from intended interventions
  3. Bias due to missing outcome data
  4. Bias in measurement of the outcome
  5. Bias in selection of the reported result

At the end of each section, an algorithm is provided to make a final judgement on the risk of bias. Each component is weighed equally to provide an overall risk of bias judgment.


Savović, J., Weeks, L., Sterne, J.A. et al. Evaluation of the Cochrane Collaboration’s tool for assessing the risk of bias in randomized trials: focus groups, online survey, proposed recommendations and their implementation. Syst Rev 3, 37 (2014). https://doi.org/10.1186/2046-4053-3-37


Reliability has not been extensively studied (BMJ), however some items are more difficult to assess by users. Ongoing guidance and training materials have been developed to help improve reliability.

These summaries are written by the NCCMT to condense and to provide an overview of the resources listed in the Registry of Methods and Tools and to give suggestions for their use in a public health context. For more information on individual methods and tools included in the review, please consult the authors/developers of the original resources.

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