Heterogeneity will be greater in a systematic review of NRS than in a systematic review of randomized trials. Therefore, authors should consider very carefully the likely extent of heterogeneity between included studies when deciding whether to pool findings quantitatively (i.e. by meta-analysis). We expect pooling of effect estimates from NRS to be the exception, rather than the rule.
Effect estimates from NRS should not be combined with effect estimates from randomized trials, or across NRS that use dissimilar study design features.
Forest plots should be used to summarize the findings from included studies.
Heterogeneity diagnostics and investigations may be used irrespective of whether or not a decision has been taken to pool effect estimates from different studies.