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Comparative Study
. 2006 May 9:6:23.
doi: 10.1186/1471-2288-6-23.

Optimizing search strategies to identify randomized controlled trials in MEDLINE

Li Zhang  1 , Isola Ajiferuke, Margaret Sampson
Affiliations
Comparative Study

Optimizing search strategies to identify randomized controlled trials in MEDLINE

Li Zhang et al. BMC Med Res Methodol. .

Abstract

Background: The Cochrane Highly Sensitive Search Strategy (HSSS), which contains three phases, is widely used to identify Randomized Controlled Trials (RCTs) in MEDLINE. Lefebvre and Clarke suggest that reviewers might consider using four revisions of the HSSS. The objective of this study is to validate these four revisions: combining the free text terms volunteer, crossover, versus, and the Medical Subject Heading CROSS-OVER STUDIES with the top two phases of the HSSS, respectively.

Methods: We replicated the subject search for 61 Cochrane reviews. The included studies of each review that were indexed in MEDLINE were pooled together by review and then combined with the subject search and each of the four proposed search strategies, the top two phases of the HSSS, and all three phases of the HSSS. These retrievals were used to calculate the sensitivity and precision of each of the six search strategies for each review.

Results: Across the 61 reviews, the search term versus combined with the top two phases of the HSSS was able to find 3 more included studies than the top two phases of the HSSS alone, or in combination with any of the other proposed search terms, but at the expense of missing 56 relevant articles that would be found if all three phases of the HSSS were used. The estimated time needed to finish a review is 1086 hours for all three phases of the HSSS, 823 hours for the strategy versus, 818 hours for the first two phases of the HSSS or any of the other three proposed strategies.

Conclusion: This study shows that compared to the first two phases of the HSSS, adding the term versus to the top two phases of the HSSS balances the sensitivity and precision in the reviews studied here to some extent but the differences are very small. It is well known that missing relevant studies may result in bias in systematic reviews. Reviewers need to weigh the trade-offs when selecting the search strategies for identifying RCTs in MEDLINE.

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Figures

Figure 1
Figure 1
Steps of how sensitivity and precision were calculated. Note 1. The number of the pooled studies of each SR is the denominator of the sensitivity for each SR. Note 2. The number of items retrieved in this step is the nominator of the sensitivity and the precision for each SR. Note 3. The number of items retrieved in this step is the initial search output (articles needed to screen) of a SR, which is also the denominator of the precision. SR = systematic review
Figure 2
Figure 2
Formula for calculating sensitivity and precision.
Figure 3
Figure 3
Flow of systematic reviews through the phase of screening and eligibility evaluation. * For some reviews, more than one exclusion criteria was noted, therefore numbers do not add up to 73.
See this image and copyright information in PMC

References

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