Optimizing the literature search: coverage of included references in systematic reviews in Medline and Embase
Keywords:Systematic reviews, Literature search, Databases, Medline, Embase, Cross-sectional study
Objective: The aim of this study was to investigate if the included references in a set of completed systematic reviews are indexed in Ovid MEDLINE and Ovid Embase, and how many references would be missed if we were to constrict our literature searches to one of these sources, or the two databases in combination.
Methods: We conducted a cross-sectional study where we searched for each included reference (n = 4,709) in 274 reviews produced by the Norwegian Institute of Public Health to find out if the references were indexed in the respective databases. The data was recorded in an Excel spreadsheet where we calculated the indexing rate. The reviews were sorted into eight categories to see if the indexing rate differs from subject to subject.
Results: The indexing rate in MEDLINE (86.6%) was slightly lower than in Embase (88.2%). Without the MEDLINE records in Embase, the indexing rate in Embase was 71.8%. The highest indexing rate was achieved by combining both databases (90.2%). The indexing rate was highest in the category "Physical health - treatment" (97.4%). The category "Welfare" had the lowest indexing rate (58.9%).
Conclusion: Our data reveals that 9.8% of the references are not indexed in either database. Furthermore, in 5% of the reviews, the indexing rate was 50% or lower.
Higgins J, Thomas J, Chandler J, Cumpston M, Li T, Page M, Welch V. Cochrane Handbook for Systematic Reviews of Interventions version 6.2 [Internet]. Cochrane; 2021 [cited 1 Feb, 2021]. .
Folkehelseinstituttet. Slik oppsummerer vi forskning: håndbok for Folkehelseinstituttet. Oslo: FHI; 2018.
Frandsen TF, Gildberg FA, Tingleff EB. Searching for qualitative health research required several databases and alternative search strategies: a study of coverage in bibliographic databases. J Clin Epidemiol. 2019;114:118-24. DOI: 10.1016/j.jclinepi.2019.06.013
Frandsen TF, Eriksen MB, Hammer DMG, Christensen JB. PubMed coverage varied across specialties and over time: a large-scale study of included studies in Cochrane reviews. J Clin Epidemiol. 2019;112:59-66. DOI: 10.1016/j.jclinepi.2019.04.015
Frandsen TF, Eriksen MB, Hammer DMG, Christensen JB, Wallin JA. Using Embase as a supplement to PubMed in Cochrane reviews differed across fields. J Clin Epidemiol. 2021;133:24-31. DOI: 10.1016/j.jclinepi.2020.12.022
Johansen M, Paulsen E, Fønhus MS, Miller P. What if EPOC reviews only included studies from MEDLINE? Presented at: 25th Cochrane Colloquium; Edinburgh, Scotland 16-18 Sept, 2018.
Bramer WM, Rethlefsen ML, Kleijnen J, Franco OH. Optimal database combinations for literature searches in systematic reviews: a prospective exploratory study. Syst Rev. 2017;6(1):245. DOI: 10.1186/s13643-017-0644-y
Bramer WM, Giustini D, Kramer BM. Comparing the coverage, recall, and precision of searches for 120 systematic reviews in Embase, MEDLINE, and Google Scholar: a prospective study. Syst Rev. 2016;5:39. DOI: 10.1186/s13643-016-0215-7
Mathisen M. Evaluating and optimizing the search process for systematic reviews (Doctoral thesis). Oslo: OsloMet; 2021.
Svanberg T, Stadig I. Databases used for systematic reviews – how much is enough? Presented at: EAHIL; Lodz, Poland 16-18 Nov, 2020.
Halladay CW, Trikalinos TA, Schmid IT, Schmid CH, Dahabreh IJ. Using data sources beyond PubMed has a modest impact on the results of systematic reviews of therapeutic interventions. J Clin Epidemiol. 2015;68(9):1076-84. DOI: 10.1016/j.jclinepi.2014.12.017
Hartling L, Featherstone R, Nuspl M, Shave K, Dryden DM, Vandermeer B. The contribution of databases to the results of systematic reviews: a cross-sectional study. BMC Med Res Methodol. 2016;16(1):127. DOI: 10.1186/s12874-016-0232-1
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