Considerations from the risk of bias perspective for updating Cochrane reviews.

Authors of Cochrane reviews are expected to update their reviews every 2 years. The updating process helps to ensure that reviews are current and include recent evidence. However, the updating process is time-consuming for authors, particularly when Cochrane methods evolve and authors are required to revisit some of the originally included studies.The Cochrane Collaboration's 'Risk of bias' tool is a mandatory component of Cochrane reviews, providing an assessment of the potential biases of included studies. The tool has been modified most recently in 2011, and the expectation is that new versions will continue to be produced and utilised in all Cochrane reviews. In this commentary we discuss, in the context of updating scenarios that are likely to be encountered, the potential options systematic review authors may have recourse to when the Cochrane Collaboration's 'Risk of bias' tool has been modified between the original review and its update. We recommend that authors who are updating reviews should revise their original assessments of included studies using the most recent version of the risk of bias tool. Despite the increased workload, use of the most recent version of the tool facilitates consistency of methods and reporting both across and within reviews, and ensures currency to the methodological rigour.