What RoB 2 is
RoB 2 is the Cochrane tool for assessing risk of bias in randomized trials (Sterne JAC et al. BMJ 2019;366:l4898). It replaced the 2011 tool (RoB 1) in Cochrane reviews. You judge one specific result of each trial, not the trial as a whole, across five domains.
If your protocol names RoB 1, the older tool, pick it in the instrument list: it has seven domains, including blinding and “other bias”, and its judgements are low, unclear or high risk.
The five RoB 2 domains
In the tool’s own words; on the figure they are D1 to D5.
- D1 Bias arising from the randomization process
- D2 Bias due to deviations from intended interventions
- D3 Bias due to missing outcome data
- D4 Bias in measurement of the outcome
- D5 Bias in selection of the reported result
Low risk · Some concerns · High risk. Grey: cells not filled in yet.
Judgements and the overall judgement
Each domain is low risk, some concerns or high risk. “No information” is not a RoB 2 level: the figure draws it grey for cells you have not filled in yet.
The overall judgement follows the worst domain: low risk only if every domain is low; some concerns if any domain has some concerns and none is high; high risk if any domain is high. RoB 2 also allows an overall high when several concerns together substantially lower confidence. The “Fill in the overall judgement” button applies the mechanical rule and leaves that call to you.
How to make the RoB 2 figure
- The table above is already set to RoB 2. Replace the example studies with yours, or paste the table from Excel or Google Sheets (the robvis template works).
- Pick the judgement for each domain and, if the instrument has one, press “Fill in the overall judgement” and correct what needs correcting.
- Download the traffic light plot, the summary plot or both: PDF or SVG when the journal wants vector artwork; PNG or TIFF at the column width and 300 or 600 dpi when it wants an image.
Frequently asked questions
Is RoB 2 the Cochrane risk of bias tool?
Yes, it is the current version. The first one, from 2011 (RoB 1), had seven domains and still appears in older reviews and in RevMan. Both are in the instrument list on this page.
What are the five domains of RoB 2?
Bias arising from the randomization process; bias due to deviations from intended interventions; bias due to missing outcome data; bias in measurement of the outcome; and bias in selection of the reported result.
What do I enter when the paper says nothing about a domain?
In RoB 2 missing information is not a level: “no information” is an answer to the signalling questions, and depending on which ones get it the algorithm can reach any level, often some concerns. Until you decide, the cell stays grey.
Can I use the figure in my paper?
Yes. Unless you are signed in to a revisia account with a verified email, what you download carries a small revisia mark under the figure, outside the drawing. With a verified email the figure comes out clean, in the preview and in every format. The account is free.