There may be occasions when, in addition to re-executing the search, an update to a review also involves a change to the review question, the study selection criteria, or both. For example, evolving technology may lead to the inclusion of a new comparison; or a category of patients (e.g. children in addition to adults) or an important outcome (e.g. adverse effects) may not have been adequately addressed in the original review. If this is the case, the proposed changes and additions to the original protocol should be documented and justified in the ‘Differences between protocol and review’ section, explained in the text of the review (Background, Objectives and Methods sections) and highlighted in the ‘What’s new’ table.
In addition, the search methods may need to be altered and re-executed to cover not only the period since the ‘Date of search’ of the previous version of the review, but also the period covered by the original review with the addition of new search terms relevant to any additional selection criteria. In some cases it may be sufficient to go back to the original search results and apply the updated selection criteria for inclusion of studies.
If a new comparison or a new outcome has been added to the review, it will be necessary to go back to the original included studies and check that they did not include any information relevant to this new outcome or comparison. The original data collection forms may need to be altered or extended, and piloted again, and new comparisons or outcomes may have to be added to the analyses.
Finally, the addition of new comparisons, populations or outcomes will result in the need for alteration of the text of the review (Background, Methods) and, if additional studies are identified and included, also to the Results, Conclusions, 'Plain language summary' and ‘Summary of findings’ table.