Key points:

• Before undertaking an update, authors should consider the currency and relevance of the question, as well as the methodology used to address it.
• A new protocol will be required if important changes are made to the review question or the general methodology. 
• An update should be conducted according to the standards required for any review, with the following additional requirements to ensure that any changes are managed appropriately and reported clearly to readers

Since its inception, Cochrane has advocated for the routine updating of systematic reviews, in order to take account of new evidence. However, before undertaking an update, it is important to consider carefully whether an update is warranted. See Handbook Chapter IV, section 2 for a framework and checklist on deciding whether or when to update a Cochrane Review. All CRGs are encouraged to classify their reviews by their update status, to denote whether the review is up to date, an update is pending or no update is planned (see the Updating Classification System).

Several important decisions are required at the beginning of the planning of an update. The first is whether the original review question is still relevant. The second is whether the general methodological approach is still appropriate to answer the review question: this will need a review of the original protocol. Third, authors need to address whether the scope of the review is appropriate, whether it should be split into two or more reviews, or whether it should be merged with other reviews. Important changes of this nature indicate a need for a new protocol. 

The following updating standards reflect two key stages: planning and conducting the update. Expectations are that review authors will consider each of these sections before updating a review.   Authors should examine and address any feedback on the original review before embarking on an update or a new derivative review. Planning an update should involve discussion with the Cochrane Review Group (CRG) over the adoption of new methods or changes to the review question proposed. The following standards for updates should be used in conjunction with the conduct and reporting standards for new Cochrane Reviews and these are cited where necessary. 

Jackie Chandler
Methods Co-ordinator (2011-2018)
Cochrane Editorial and Methods Department