If your systematic review search returns too few results, first verify that your search strategy isn't overly restrictive, then systematically broaden it while maintaining methodological rigor.
Check Your Search Construction
Start by reviewing your Boolean operators and syntax. An AND between all terms creates a very narrow search—if you're searching "diabetes AND exercise AND elderly AND cardiovascular outcomes," you're requiring all four concepts to appear together. Consider whether all terms are truly essential or if some could be combined with OR to capture similar concepts (e.g., "elderly OR older adults OR aged").
Examine your filters as well. Restricting to only the last five years, English-only, or specific publication types may exclude relevant foundational studies. Systematic reviews typically cast a wide net initially, then apply exclusion criteria during screening rather than at the search stage.
Expand Your Search Systematically
If your core search is sound but still yields insufficient results, broaden strategically:
Add synonym variations: Medical Subject Headings (MeSH) and keyword variations matter. "Myocardial infarction" versus "heart attack" versus "MI" can return different paper sets.
Include adjacent concepts: If searching "telemedicine for diabetes management" returns little, consider expanding to "remote monitoring" or "digital health interventions."
Search additional databases: Don't rely solely on PubMed. Scopus, Web of Science, IEEE Xplore (for technology-related topics), and discipline-specific databases often index different journals. WisPaper's Scholar Search covers 360M+ papers across 32 disciplines with intent-based matching that understands complex inclusion logic, which can help surface relevant papers that pure keyword searches miss.
Review reference lists: Conduct backward citation searching on the few papers you did find—their bibliographies often lead to foundational work your search missed.
Document Everything
Whatever changes you make, document them in your PRISMA flow diagram. Systematic reviews require transparency about search evolution. Note which databases you searched, what terms you tested, and why you modified your strategy. This documentation demonstrates methodological soundness even when your final included studies number is modest—sometimes a small evidence base simply reflects a genuinely under-researched question.
