Development and validation of a geographic search filter for PubMed for retrieving studies about Nordic countries.

Objective: This study describes the development and validation of a geographic search filter. The filter is intended to find references on the Nordic countries in PubMed. This type of filter enables efficient systematic literature searches for evidence that is relevant for the region, and no validated filter for these countries is publicly available at the time of this publication. Methods: The Nordic countries are Denmark, Finland, Iceland, Norway and Sweden. References on one or more of these countries were identified by relative recall, using systematic and scoping reviews that did not limit searches to any geographic region but presented the countries of included studies. The references (n = 288) were equally split into a development set and a validation set. A combination of objective and subjective methods was used to identify relevant terms from the development set. The filter was then tested, first on the development set, then on the validation set. A sample of the reviews that were used to identify references for recall testing was also used to test precision. Results: The final filter surpassed the threshold recall of 90%. Recall was 94.4% for the development set, capturing 136 of 144 references, and 96.5% for the validation set, or 139 of 144. Precision was 95.8% with one false positive of 24 retrieved references. Conclusions: A validated filter has been developed that can be used to find studies on the Nordic countries when searching PubMed on topics related to human health.