Supplementary strategies identified additional eligible studies in qualitative systematic reviews

Background and Objectives: There is an increasing number of qualitative systematic reviews being produced. Searching for qualitative literature to include in these systematic reviews is, however, more challenging and may result in less than favorable recall. Database searches relying solely on key elements of the research question may not retrieve all relevant qualitative studies for synthesis, and supplementary searches may be pertinent to complement the searches. This study aimed to determine, if a) supplementary search strategies (citation searches and alternative search strategies) were able to identify relevant publications for qualitative systematic reviews that were nonretrievable, when conducting traditional database searches based on key elements; and b) to investigate the total number of identified publications when combining traditional database searches with these supplementary search strategies. Methods: From a previous study, a gold standard of 12 qualitative reviews including 101 PubMed-indexed publications was used. One of the reviews had only one included publication and in one review, the two included studies were identifiable in PubMed. In the remaining 10 reviews, 61 publications were retrievable through traditional database searches, and 37 were nonidentifiable. The 61 publications were used as basis for possible identification of the 37 publications by using the supplementary search strategies: citations searches (review of reference lists, PubMed “Cited by” function; Scopus “Cited by” function, Citationchaser, CoCites plugin for PubMed) and alternative search strategies (PubMed “similar articles” function; Scopus “Related documents based on references”). Results: Traditional database searches retrieved 62.4% of the 101 publications. Citations searches in Scopus, Citationchaser and CoCites identified 21 (56.8%) of the 37 remaining publications. The PubMed “Cited by” function did not identify any of the 37 publications. The alternative search strategies, the PubMed “Similar articles” together with Scopus “Related documents based on references”-function) identified 15 (40.5%) of the 37 publications. Together, these supplementary search strategies identified 25 (67.6%) of the 37 publications, resulting in an overall retrieval of 87.1%, when combining traditional database searches and supplementary search strategies. Conclusion: The results of this study indicate that supplementary search strategies (citation searches and alternative search strategies) increase the retrieval potential, when searching for qualitative publications and should be included, when identifying literature for qualitative reviews.