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The Cochrane Library: An Important Resource for Evidence Based Medicine
Johnson Francis, MD, DM* Steve McDonald **
*Associate Professor of Cardiology and Associate Editor-Calicut
Medical Journal, Medical College Calicut, Kerala, India.
**Research Fellow, Australasian Cochrane Centre, Monash University, Australia.
Address for Correspondence:
Dr. Johnson Francis, MD, DM,
Pulikkottil, Thondayad,
P.O. Chevarambalam,
Calicut -673017,
Kerala, India.
Phone: +91-495-2356888
Email: pulikkottil2002@hotmail.com
This is the era of evidence based medicine. We are faced with an abundance of information, much of which is conflicting, that we must contend with if we are to arrive at the most appropriate treatment for the individual patient. Integrating the best research evidence with clinical expertise and patient values is the essence of evidence based practice. Systematic reviews of the existing literature assume paramount importance in this scenario. Archie Cochrane, a British epidemiologist, recognised that without the ability to access the best available evidence, important information about the effects of health care, both good and bad, would be missed. He was instrumental in highlighting that health care practice is not always based on good evidence and was critical of the medical profession for failing to seek evidence to support treatment recommendations.[1] In response to this challenge, the Cochrane Collaboration was founded in 1993 to prepare and promote the use of systematic reviews in health care. In the space of a decade, the Cochrane Collaboration
(www.cochrane.org) has grown remarkably and now has centres in 12 countries, 50 topic-based Collaborative Review Groups and over 7000 members representing 80 countries.
The main output of the Cochrane Collaboration is the Cochrane Library (www.thecochranelibrary.com)
. As the name suggests, the Library is a collection of resources and aims to bring together reliable information about the effects of health care interventions. The most important of these resources is the Cochrane Database of Systematic Reviews, a rapidly expanding collection of nearly 2000 full-text reviews. Cochrane reviews bring together information on controlled studies (mostly from randomised trials) in a standard format and are published successively in each quarterly issue of the Cochrane Library. A key feature of Cochrane reviews is that, unlike reviews published in journals, they can be regularly updated to take account of new evidence. Indeed, Cochrane reviewers are obliged to update their reviews every two years. Another important database in the Cochrane Library is the Cochrane Central Register of Controlled Trials (CENTRAL). With over 400,000 reports, CENTRAL is regarded as the single best source of controlled trials and is used extensively by reviewers to identify studies relevant to their reviews.
Cochrane reviews are produced in a systematic manner and follow several predefined steps.[2] A reviewer intending to conduct a review first contacts the relevant Collaborative Review Group to register a topic or title. Provided the topic is available the next step is to prepare a protocol for the review. The protocol describes the rationale and objectives of the review and sets out the methodology the reviewers will follow, including precise inclusion criteria for eligible studies and the outcomes to be reported. Protocols are an important step in minimising bias because reviewers must consider the methodological issues before they begin reviewing relevant studies. Like reviews, protocols are also published in the Cochrane Library following editorial and peer review.
Once the protocol is published the search for studies begins. With the help of a dedicated member of the review group, search strategies are designed for major bibliographic databases like CENTRAL, MEDLINE and EMBASE as well as any relevant subject specific databases. However the search for studies is not only restricted to electronic sources. It is well known that studies with negative results are less likely to be published as full reports and those that are, tend to be published in smaller less accessible journals. To address this concern, the Cochrane Collaboration has invested substantial effort in the manual searching of several thousand journals, conference proceedings and other grey literature sources irrespective of the language of publication. Studies identified through handsearching are then added to CENTRAL in the Cochrane Library.[3] Furthermore, the reference lists of retrieved articles are checked to identify further relevant studies and investigators of included trials are often contacted for data missing from the published report.
Studies meeting the inclusion criteria for the review are assessed carefully for their methodological quality and only those deemed to be sufficiently rigorous are included in the review. Studies that are excluded are listed separately in the published review together with the reasons for their exclusion. Data extracted from the studies meeting the inclusion criteria are analysed according to the methods described in the protocol. Any deviation from the published protocol may introduce bias and has to be adequately justified. Data from the individual studies may be combined in the form of a meta-analysis or statistical synthesis, however, the decision to pool the data in this way is made following an assessment of how similar the studies are. If studies are too heterogeneous (either clinically or statistically) then reviewers may decide to limit their analysis to a description of the results and not include a formal meta-analysis.
A typical Cochrane review contains six included studies and although the vast majority of these are randomised trials, a growing number incorporate non-randomised evidence.[4] This is the case, for example, when reviews address questions outside the scope of randomised trials. Cochrane reviews are primarily a tool to inform clinical practice but they also play an important role in informing the research agenda. Reviews without any included trials or that present inconclusive evidence indicate to researchers and major public funding agencies where further trials are needed.
With the support of the Australasian Cochrane Centre, efforts are now underway to establish a Cochrane network in India and South Asia. The number of reviewers from the region has increased steadily in recent years, however it is clear that if India and other countries in South Asia are to play a full part in the growth of the Collaboration during the next decade and beyond, then there needs to be adequate access to training and support locally. As a first step in this process, a dedicated mailing list and web page has recently been established by one of the authors.[5]
Much has been achieved by the Collaboration in its first ten years, but equally many challenges remain. Enabling wide participation and striving for relevance are two of the Collaboration's ten principles that are especially applicable to South Asia. With an estimated 10,000 to 12,000 more reviews needed to cover the existing evidence on the effects of healthcare interventions [6], there is plenty of scope for reviewers in this region to participate and help ensure that Cochrane reviews address issues that are relevant to local users and practitioners.
References
1. Chalmers I, Dickersin K, Chalmers TC. Getting to grips with Archie Cochrane's agenda. BMJ 1992;305:786-8.
2. Alderson P, Green S, Higgins JPT (eds). Cochrane Reviewers' Handbook 4.2.1 [updated December 2003].
http://www.cochrane.org/resources/handbook/hbook.htm
.
3. Dickersin K, Manheimer E, Wieland L, Robinson K, Lefebvre C, McDonald S. Development of the Cochrane Collabration's Central register of controlled clinical trials. Evaluation and the Health Professions 2002;25:38-64.
4. Mallett S, Clarke M. The typical Cochrane review: how many trials? How many participants? International Journal of Technology Assessment in Health Care;18:820-23.
5. South Asian page of the Australasian Cochrane Centre. http://www.cochrane.org.au/region/southasia.htm
6. Mallet S, Clarke M. How many Cochrane reviews are needed to cover the existing evidence on the effects of healthcare interventions? Evidence Based Medicine 2003;8:100-1.
Source of Funding:
There was no grant support for this article
| This
is a non-peer reviewed article. Accepted for publication on
April 2,2004
Cite
as:
Francis
J,McDonald S.The Cochrane Library: An Important Resource for Evidence Based Medicine
Calicut
Medical Journal 2004;2(2):e1
URL: http://www.calicutmedicaljournal.org/2004/2/2/e1
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