Value of using different search approaches

Authors

Elke Hausner

Christopher Cooper

Ingrid Harboe

Nick Halfpenny

Siw Waffenschmidt

Ruth Wong

Last updated: 29 October 2021

What's new in this update

No new research relevant to the chapter was identified during the October 2021 update.

Introduction

The conventional search approach of applying Boolean logic to subject heading and free-text queries continues to dominate literature reviews as it remains an effective method for searching bibliographic databases. However, sensitivity and specificity issues relating to Boolean searching have led researchers to investigate a variety of alternative search approaches: citation searching (direct or indirect citation relationships), the use of the “similar articles” function, hand searching, and methods of automated retrieval are some examples.

Similar articles

There is evidence that the “similar articles” link in PubMed (formerly known as “related citations”) is an efficient search approach (1-3) that can be used for scoping searches or for identifying the need to update a systematic review. The results of three analyses suggest that there is real benefit in using the 'similar articles' link and a simple Boolean search in PubMed. In the study by Waffenschmidt et al (3) the combination of these two search methods resulted in 98% sensitivity when searching for randomized controlled trials (RCTs) of drugs. Sampson et al searched for various topics and the combination of the two search methods reached 90% sensitivity in the original testing (1) and 91% (2) when retested.

Citation searching

How well citation searching works depends on whether the citation network between articles is closed. Robinson et al. (4) examined citation networks of related trials and evaluated 259 meta-analyses. They concluded that citation networks are often disconnected. However, they only checked citation links between RCTs; especially in the case of indirect citation relationships, all citations in a reference list should be analysed.

Direct citation relationships: Checking reference lists and citation tracking

A review article by Cooper et al. (5) discusses the current literature on supplementary search techniques, such as citation searching, including the advantages and disadvantages of these techniques.

A Cochrane review (6) included 12 studies examining manually checking reference lists and concluded that there is some evidence to support this method when traditional searching is difficult, but that the studies were heterogeneous and at a high risk of bias. A recent study by Preston et al. (7) showed that search strategies in MEDLINE and Embase identified 85% of studies on diagnostic test accuracy included in 9 systematic reviews; 24 further studies (8%) were identified by checking reference lists. A single study (8) comparing an automated system using the Scopus database with manual reference checking found the automated system to be equally sensitive but considerably more (62.5%) time efficient than the manual method.

Citation tracking (e.g. “cited by” function in Google Scholar) seems to identify only few additional references when used in addition to traditional searching. Four case studies of systematic or scoping reviews (9-12) showed that citation tracking as a supplementary approach found between 0 and 14% more unique references. However, citation tracking appears to offer some added value compared with Boolean searching when performing more challenging searches (e.g. for outcome measures) (13).

Indirect citation relationships: Co-citations searching

Since 2015, four studies have assessed the co-citations (i.e. the reference lists of articles citing key articles) of systematic or meta-analyses (sample size between 10 and 250) across a range of topics. Janssens and Gwinn (14) analysed co-citations and found that sensitivities between 79 and 82% were achieved when combining co-citation searching and direct citation searching. The number needed to screen (NNS) was reduced by 50 to 89% (median) compared with traditional searching. The approach was validated in a subsequent study (15) and achieved a median sensitivity of 75%. The CoCites tool was recently released for public use (16).

Belter (17, 18) used a combination of approaches (similar articles, direct and indirect citation relationships) in the Web of Science database. He tested and modified the method in two studies and retrieved a median of 74 to 87% of the references included in Cochrane reviews.

Full-text search

Linder (13) evaluated Google Scholar's full-text search feature in order to find studies on 'outcome measurement instruments' - terms that are often omitted from the title, abstract and subject headings of articles. The keyword (full text) search using Google Scholar yielded the highest sensitivity (70%). However, one must bear in mind that searching Google Scholar is time-consuming and difficult, as its functionality (e.g. incomplete bibliographic information, no reference export) remains limited (19).

Automated retrieval methods

At present automated retrieval methods implemented e.g. in public available interfaces have not been sufficiently evaluated to decide whether they are a useful approach for performing sensitive searches. One study comparing Boolean searching with ranked querying in MEDLINE (Ovid) reported that ranked retrieval alone was not reliable for a search task requiring high recall (20, 21).

Hand searching

Several current studies comparing hand searching with electronic database searching concluded that there was little or no benefit offered by hand searching. This was found to be the case when searching for additional RCTs (22), diagnostic test accuracy (DTA) studies (23), and occupational health intervention studies published in a language other than English (24). This contradicts the conclusions of a 2007 Cochrane review which found hand searching to be an effective approach when searching for systematic reviews; however, this review is now outdated as its most recent search was performed in 2002 and its main comparison was between hand searching and the "old" (1994), three-section Cochrane Highly Sensitive Search Strategy for RCTs (25).

Reference list

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(2) Sampson M. Complementary approaches to searching MEDLINE may be sufficient for updating existing systematic reviews. J Clin Epidemiol. 2016;78:108-15. [Publication appraisal]

(3) Waffenschmidt S, Janzen T, Hausner E, Kaiser T. Simple search techniques in PubMed are potentially suitable for evaluating the completeness of systematic reviews. J Clin Epidemiol. 2013;66(6):660-5. [Publication appraisal]

(4) Robinson KA, Dunn AG, Tsafnat G, Glasziou P. Citation networks of related trials are often disconnected: implications for bidirectional citation searches. J Clin Epidemiol 2014. p. 793-9. [Publication appraisal]

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How to cite this chapter:

Hausner E, Waffenschmidt S. Value of using different search approaches. Last updated 29 October 2021. In: SuRe Info: Summarized Research in Information Retrieval for HTA. Available from: https://www.sure-info.org//value-of-using-different-search-approaches



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