Background: Scoping reviews (ScRs) aim to comprehensively map available evidence on a particular topic, and both primary studies and systematic reviews (SRs) may be eligible for inclusion. For well-developed topics, primary studies are usually included in the often numerous SRs available, and thus, restricting scoping to SRs may be sufficient, particularly if these include recent SRs. For less well-developed topics, a balance between including SRs and primary studies may be needed to ensure adequate representation of the available evidence, while maintaining efficiency. Objective: To describe a two-tiered search strategy for time-sensitive ScRs where different considerations necessitated tiered searching. The ScR topics included lesser-known interventions with scant evidence or new interventions and settings with an immature evidence base and limited synthesised evidence.
Methods: We developed and applied two-tiered searching in two time-sensitive ScRs for World Health Organization (WHO) nutrition guidelines, supported by an information specialist. Comprehensive a priori frameworks of all possibly eligible interventions were developed. The first-tier search was limited to SRs. Following data extraction, the frameworks were used for gap analyses identifying interventions or strategies not covered by the eligible SRs. These analyses informed the targeted second-tier searches to identify eligible primary studies addressing these gaps.
Results: After including eligible SRs, the frameworks enabled quick identification of eligible interventions or strategies not covered by SR evidence. The first-tier search resulted in 15 eligible SRs (from yield n=492) and the second-tier search in 12 eligible primary studies (from yield n=1,699) for one ScR. For the other ScR, the first-tier search resulted in 69 eligible SRs (from yield n=1,448) and the second-tier search in 24 eligible primary studies (from yield n=545). This tiered approach produced manageable yields and improved efficiency when compared with broad searching for SRs and primary studies across multiple interventions, which often results in prohibitively high yields.
Conclusions: This strategy enabled the efficient production of comprehensive ScRs informing the prioritisation of key guideline questions within time-sensitive policy windows.
Patient, public and/or healthcare consumer involvement: No direct involvement. The ScRs are informing WHO public health nutrition guidelines aimed at achieving the best health outcomes possible for the public.