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. 2018 Nov 20;7(1):200.
doi: 10.1186/s13643-018-0864-9.

Searching Embase and MEDLINE by using only major descriptors or title and abstract fields: a prospective exploratory study

Wichor M Bramer  1 , Dean Giustini  2 , Jos Kleijnen  3   4 , Oscar H Franco  5   6
Affiliations

Searching Embase and MEDLINE by using only major descriptors or title and abstract fields: a prospective exploratory study

Wichor M Bramer et al. Syst Rev. .

Abstract

Background: Researchers performing systematic reviews (SRs) must carefully consider the relevance of thousands of citations retrieved from bibliographic database searches, the majority of which will be excluded later on close inspection. Well-developed bibliographic searches are generally created with thesaurus or index terms in combination with keywords found in the title and/or abstract fields of citation records. Records in the bibliographic database Embase contain many more thesaurus terms than MEDLINE. Here, we aim to examine how limiting searches to major thesaurus terms (in MEDLINE called focus terms) in Embase and MEDLINE as well as limiting to words in the title and abstract fields of those databases affects the overall recall of SR searches.

Methods: To examine the impact of using search techniques aimed at higher precision, we analyzed previously completed SRs and focused our original searches to major thesaurus terms or terms in title and/or abstract only in Embase.com or in Embase.com and MEDLINE (Ovid) combined. We examined the total number of search results in both Embase and MEDLINE and checked whether included references were retrieved by these more focused approaches.

Results: For 73 SRs, we limited Embase searches to major terms only while keeping the search in MEDLINE and other databases such as Web of Science as they were. The overall search yield (or total number of search results) was reduced by 8%. Six reviews (9%) lost more than 5% of the relevant references. Limiting Embase and MEDLINE to major thesaurus terms, the number of references was 13% lower. For 15% of the reviews, the loss of relevant references was more than 5%. Searching Embase for title and abstract caused a loss of more than 5% in 16 reviews (22%), while limiting Embase and MEDLINE that way this happened in 24 reviews (33%).

Conclusions: Of the four search options, two options substantially reduced the overall search yield. However, this also resulted in a greater chance of losing relevant references, even though many references were still found in other databases such as Web of Science.

Keywords: Bibliographic; Databases; Information storage and retrieval; Review literature as topic; Sensitivity and specificity.

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Figures

Fig. 1
Fig. 1
Flow chart of references included and found by focused searches
Fig. 2
Fig. 2
Percentage of reviews that reached a certain recall threshold using focused searches
Fig. 3
Fig. 3
Ratio between total number of search results for systematic reviews for focused searches and the original unchanged searches. The figure shows from left to right: minimum, 10th percentile, 25th percentile, average, median, 75th percentile, 90th percentile, and maximum
Fig. 4
Fig. 4
The sensitivity of searches for all databases where Embase was focused to major thesaurus terms for different review types and topics
Fig. 5
Fig. 5
The effect of the four focused search methods on therapeutic reviews that included only RCTs (N = 10)
Fig. 6
Fig. 6
The effect of the four focused search methods on reviews about oncology (N = 5)
See this image and copyright information in PMC

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