Geographic search filters: promising tools for contextualizing research

Geography is an important dimension in medical and health research, enabling the analysis of spatial patterns in disease distribution, environmental exposures, and health care systems. A regional perspective on health care can reveal differences in access, quality, and outcomes, which are critical for understanding and addressing health inequalities within and between regions. The geographical context is also an important factor in understanding how interventions are received and implemented. In health economics, geographic delimitations can help uncover differences in health care expenditure, resource allocation, and cost-effectiveness across regions. Moreover, a geographically focused approach allows exploration of cultural influences on health behavior and care practices, offering insights into how cultural contexts shape health care delivery and outcomes.1 When conducting a search in bibliographic databases such as PubMed, it can be beneficial to limit the search by geographical features to obtain context-specific results. Currently, at least 3 different approaches to geographically limit literature searches are typically used. First, it is possible to conduct the literature search without applying any geographic restrictions. While this yields a broad range of hits, it also results in many irrelevant records that do not relate to the geographic context. This increases the screening workload considerably, as researchers must manually identify which records are relevant. Second, using only the country name as a search term can lead to missing relevant records for several reasons. Countries may be referred to in different ways across records, for example, through abbreviations (eg, US or USA) or full official names (eg, United States of America instead of United States). Additionally, some records may not mention the country at all, instead referencing more specific geographical locations such as cities, provinces, or states. Third, the author affiliations listed in a publication can sometimes provide clues about the location where a study was conducted; however, this approach presents profound limitations. Authors may conduct research in regions that are different to those where they are institutionally based, especially in the context of international or multicenter projects. Moreover, many researchers hold multiple affiliations simultaneously, for example, through collaborations or visiting appointments. Relying solely on affiliation data is, therefore, insufficient.1 Robust filtering mechanisms are required to ensure comprehensive retrieval of relevant literature while avoiding an excess of non-relevant hits. Geographic search filters, described as “a collection of search terms designed to retrieve research with a common geographic feature from bibliographic databases,”2(p.200) are useful tools for limiting literature searches in order to not overlook important relevant records. Using a geographic search filter restricts literature search results to a specific spatial feature, such as a country or region. In doing so, they contribute to the contextualization of scientific evidence. The practical value of geographic search filters lies in their applicability to any scientific question confined to a specific geographical feature. Beyond their use in evidence syntheses, geographic search filters serve as valuable tools for drafting discussion sections of reports, particularly for contextualizing findings, and for informing the design of new studies; for example, they facilitate the identification of research gaps within particular geographic areas. Careful development and validation of a search filter are important, as these steps provide information about the search filter’s performance and generalizability. Validation means that a search filter has been systematically tested and proven to retrieve relevant evidence against an independent set of relevant references outside of the one used for developing the search filter. The retrieval performance of the filters can be evaluated in terms of sensitivity (also referred to as recall), precision, specificity, and number needed to read (NNR).3-6 This process ensures that a filter consistently identifies records that meet predefined criteria, while minimizing the inclusion of irrelevant studies. Equally important is how these steps are reported. Without clear and comprehensive reporting, even well-designed filters become difficult to assess for methodological rigor, replicate in further studies, or apply in real-world evidence syntheses. Furthermore, transparent reporting helps clarify the scope of the topic a filter is intended to cover, which is a key factor in determining its relevance to specific research questions.7 Our scoping review8 revealed that geographic search filters are currently not widely available. We identified only 9 reports describing 6 validated geographic filters for the following geographic features: Spain,9 Africa,10 the United Kingdom,2,11,12 Organisation for Economic Co-operation and Development countries as a group,13,14 the United States,15 and publications in high-ranking nursing journals from German-speaking countries.16 A further validated search filter for Germany has recently been introduced.17 Nevertheless, this low number is striking, considering how frequently regional differences in health care, epidemiology, or health policy play a central role in medical and public health research. The identified filters and the analyzed methods of their development and validation procedures can serve as an outline for the development of further geographic search filters; however, our scoping review8 should only be considered as a starting point. While our aim was not to assess reporting quality, suboptimal reporting across the identified search filter studies emerged as a recurring issue. In some cases, key details such as the platform the filter was developed for, filter limitations, and whether internal validation was conducted were missing. Furthermore, performance metrics beyond sensitivity were reported inconsistently. Similar reporting problems have been observed in other search filter reviews,3,18 highlighting the need for clearer guidance and reporting standards. Now is the time to systematically advance the development and evaluation of these tools and to ensure transparency and reproducibility of methodological approaches. Using geographic search filters supports JBI’s goal of transparent, targeted, and applicable methods.19 Ayiku et al.20 proposed 5 key steps for developing validated geographic search filters, which we have further refined.8 This work opens the door to further essential developments. Geographic search filters should be established as an integral component of methodological standards in evidence-based research. This requires clear criteria, standardized development, and validation procedures, as well as improved visibility in bibliographic databases.