Carol Lefebvre

Development of the Cochrane Collaboration’s Central Register of Controlled Clinical Trials

The Cochrane Collaboration has established a centralized database of controlled trials and other studies of health care interventions (called CENTRAL) that serves as the best available resource for all those preparing and maintaining systematic reviews or otherwise searching for trials. CENTRAL is available on The Cochrane Library. This article describes the history and methods of CENTRAL’s development and the results of an analysis of the current composition of CENTRAL. As of September 2000, CENTRAL contained almost 300,000 citations to reports of trials, contributed mainly by Cochrane Groups and Centers around the world. Development of CENTRAL has been an ambitious, scholarly undertaking and has resulted in a valuable resource: CENTRAL includes citations to controlled trials that may not be indexed in MEDLINE, EMBASE, or other bibliographic databases; citations published internationally in many languages; and citations that are available only in conference proceedings or other hard-to-access sources.

PRESS Peer Review of Electronic Search Strategies: 2015 Guideline Statement

OBJECTIVE To develop an evidence-based guideline for Peer Review of Electronic Search Strategies (PRESS) for systematic reviews (SRs), health technology assessments, and other evidence syntheses. STUDY DESIGN AND SETTING An SR, Web-based survey of experts, and consensus development forum were undertaken to identify checklists that evaluated or validated electronic literature search strategies and to determine which of their elements related to search quality or errors. RESULTS Systematic review: No new search elements were identified for addition to the existing (2008-2010) PRESS 2015 Evidence-Based Checklist, and there was no evidence refuting any of its elements. Results suggested that structured PRESS could identify search errors and improve the selection of search terms. Web-based survey of experts: Most respondents felt that peer review should be undertaken after the MEDLINE search had been prepared but before it had been translated to other databases. Consensus development forum: Of the seven original PRESS elements, six were retained: translation of the research question; Boolean and proximity operators; subject headings; text word search; spelling, syntax and line numbers; and limits and filters. The seventh (skilled translation of the search strategy to additional databases) was removed, as there was consensus that this should be left to the discretion of searchers. An updated PRESS 2015 Guideline Statement was developed, which includes the following four documents: PRESS 2015 Evidence-Based Checklist, PRESS 2015 Recommendations for Librarian Practice, PRESS 2015 Implementation Strategies, and PRESS 2015 Guideline Assessment Form. CONCLUSION The PRESS 2015 Guideline Statement should help to guide and improve the peer review of electronic literature search strategies.

Identifying systematic reviews in MEDLINE: developing an objective approach to search strategy design

Background: systematic reviews are of increasing importance to health care professionals seeking to provide evidence-based health care, because they provide systematically prepared summaries of the current state of research knowledge on the effectiveness of health care interventions. To be able to make use of them, both researchers preparing systematic reviews and health care professionals need to be able to identify systematic reviews easily. In the past, systematic reviews have been difficult to identify easily among the mass of literature labelled ‘reviews’. Search strategies have been published which were intended to provide easier access to systematic reviews and meta-analyses. These strategies, mostly devised for the MEDLINE database, have been constructed using the authors’ knowledge of the subject area, the databases and past experience. Objective: the objective of this study was to design search strategies based on a more objective approach to strategy construction. Methods: word frequencies from the titles, abstracts and subject keywords of a collection of systematic reviews of the effective health care interventions were analysed to derive a highly sensitive search strategy. Results: the proposed strategy offers 98% sensitivity in retrieving systematic reviews, while retaining a low but acceptable level of precision (20%). Other strategies with other levels of sensitivity and precision are also presented. Discussion: this study shows that a frequency analysis approach can be used to generate highly sensitive strategies which retain adequate levels of precision when retrieving systematic reviews.

The contribution of handsearching European general health care journals to the Cochrane Controlled Trials Register.

A fundamental aim of any systematic review is that all relevant studies should be identified and considered for inclusion. Limitations with searching bibliographic databases led the Cochrane Collaboration to search journals by hand for reports of trials. This article presents the results of a 3-year project to identify and make accessible reports of randomized trials published in European general health care journals. Overall, 21,620 reports of controlled trials were identified from119 journals from16 countries. More than three quarters (76%) were published in U.K. or German journals. Only 3,640 (17%) reports were indexed in MEDLINE as controlled trials, and 6,554 (30%) were not indexed in MEDLINE at all. Bibliographic details for all reports are available by searching The Cochrane Controlled Trials Register in The Cochrane Library. This project has ensured that a large proportion of trial reports not previously identifiable has been made accessible to those preparing systematic reviews.

Reporting methodological search filter performance comparisons: a literature review.

BACKGROUND Methodological search filters are tools for retrieving database records reporting studies which use a specific research method. Choosing a filter is likely to be based on filter performance data. This review examines which measures are reported, and the way that filter performance is presented, in filter comparisons. METHODS Studies were identified from the current content and pending update (2010) of a filter website. Eligible studies compared two or more methodological search filters designed to identify randomised controlled trials, diagnostic test accuracy studies, systematic reviews or economic evaluations. RESULTS Eighteen studies met the inclusion criteria. The number of filters compared in a single study ranged from 2 to 38. The most commonly reported measures were sensitivity/recall and precision. All studies displayed results in tables and gave results as percentages or proportions. Two studies supplemented results tables with graphical displays of data: a bar graph of the proportion of retrieved and missed gold standard references per filter; a forest plot of the overall sensitivity and specificity of each filter. CONCLUSIONS Sensitivity/recall and precision are the most frequently reported performance measures. This review highlights the potential for presenting results in novel and innovative ways to aid filter selection.

The use of clinical study reports to enhance the quality of systematic reviews: a survey of systematic review authors.

BackgroundClinical study reports (CSRs) are produced for marketing authorisation applications. They often contain considerably more information about, and data from, clinical trials than corresponding journal publications. Use of data from CSRs might help circumvent reporting bias, but many researchers appear to be unaware of their existence or potential value. Our survey aimed to gain insight into the level of familiarity, understanding and use of CSRs, and to raise awareness of their potential within the systematic review community. We also aimed to explore the potential barriers faced when obtaining and using CSRs in systematic reviews.MethodsOnline survey of systematic reviewers who (i) had requested or used CSRs, (ii) had considered but not used CSRs and (iii) had not considered using CSRs was conducted. Cochrane reviewers were contacted twice via the Cochrane monthly digest. Non-Cochrane reviewers were reached via journal and other website postings.ResultsOne hundred sixty respondents answered an open invitation and completed the questionnaire; 20/160 (13%) had previously requested or used CSRs and other regulatory documents, 7/160 (4%) had considered but not used CSRs and 133/160 (83%) had never considered this data source. Survey respondents mainly sought data from the European Medicines Agency (EMA) and/or the Food and Drug Administration (FDA). Motivation for using CSRs stemmed mainly from concerns about reporting bias 11/20 (55%), specifically outcome reporting bias 11/20 (55%) and publication bias 5/20 (25%). The barriers to using CSRs noted by all types of respondents included current limited access to these documents (43 respondents), the time and resources needed to obtain and include these data in evidence syntheses (n = 25) and lack of guidance about how to use these sources in systematic reviews (n = 26).ConclusionsMost respondents (irrespective of whether they had previously used them) agreed that access to CSRs is important, and suggest that further guidance on how to use and include these data would help to promote their use in future systematic reviews. Most respondents who received CSRs considered them to be valuable in their systematic review and/or meta-analysis.

When to include clinical study reports and regulatory documents in systematic reviews

Reporting bias is a major threat to the validity and credibility of systematic reviews. This article outlines the rationale for accessing clinical study reports and other regulatory documents (regulatory data) as a means of addressing reporting bias and identifies factors that may help decide whether (or not) to include regulatory data in systematic reviews. The article also describes the origins and current state of regulatory data access and summarises a survey of current systematic reviewers’ practices in considering regulatory data for inclusion in systematic reviews. How to access and extract regulatory data is not addressed. Organisations and other stakeholders such as Cochrane should encourage the use of data from clinical study reports as an important source of data in reviews of pharmaceutical interventions particularly when the intervention in question is of high importance and the risk of reporting bias is great.

European Union Contribution to an International Register of Controlled Trials

Randomized controlled trials (RCTs) involving sufficient numbers of patients are essential to distinguish reliably between important effects of many forms of health care and the effects of biases or the play of chance. It has been shown repeatedly that if systematic reviews of RCTs, updated periodically, had been made from the beginning of series of related trials, reliable treatment recommendations could have been made available earlier, and resources for research could have been used more efficiently. Reliable systematic reviews are based on as high a proportion of the relevant evidence as possible. Searches of major bibliographic databases such as MEDLINE and EMBASE have shown to miss on average 50% of the studies in a number of clinical areas, and many important European journals, especially those not published in English, are not indexed in the major databases.