Methods for meta-analysis allow quantification of direction of effect, size of effect and consistency of effect (see Chapter 9, Section 9.1). If suitable numerical data are not available for meta-analysis, or if meta-analyses are considered inappropriate, then these domains may often still be examined to provide a systematic assessment of the evidence available.
A narrative assessment of the evidence can be challenging, especially if the review includes a large number of studies; if the studies themselves examine complex interventions and outcomes; or if there is a lot of variation in the effects of the intervention. Patterns of effects, and similarities or differences between studies may therefore not be immediately obvious. Adopting a systematic approach to presentation is important to making sense of the results of a review. If a descriptive paragraph is provided for the results from each study, this should be done consistently, including the same elements of information for each study, presented in the same order. Organizing the studies into groupings or clusters is encouraged (e.g. by intervention type, population groups, setting etc) if a large number of studies (e.g. more than 20) have been included in the review, and can make the process of narratively describing the results more manageable. It can also enable identification of patterns in results, both within and between the groups that are formed.
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