Introduction to Cochrane systematic reviews

Advances in therapy for disorders such as Crohn's disease and ulcerative colitis stem from fundamental research focused on genetic mechanisms and immune responses, and on randomized controlled trials (RCTs) that determine whether new and traditional therapies are effective. The transfer of research findings into clinical practice is a slow process that is often not in keeping with actual evidence. A gap exists between care that is consistent with current evidence, and that which is actually provided to patients. Patients are sometimes not given interventions of proven benefit, while futile and even harmful interventions are frequently used. One reason for this gap in care is the variable quality of information provided to physicians. The best evidence to guide therapeutic decisions generally is derived from RCTs. The volume of RCTs has increased exponentially and physicians must rely on clinical practice guidelines, expert advice, and recommendations presented in traditional narrative review articles to keep abreast of the literature. Unfortunately, the quality of these sources is highly variable and may be poor even in high-impact journals. The obvious need for better reviews has led to the development of “systematic reviews,” which use explicit methods first to identify, select, and collect the relevant clinical research and to then critically appraise and analyze the data from this research. Specific methods are employed to ensure a comprehensive search for relevant data and avoid bias in their extraction and interpretation. Such systematic reviews provide the basis for evidence-based guidance to clinicians and patients, and also to policy makers and those who are charged with allocating scarce dollars to research and patient care. The Cochrane Collaboration is an international organization that aims to help people make well-informed decisions about healthcare by preparing, maintaining, and promoting accessible high-quality, up-to-date systematic reviews of the effects of healthcare interventions. Over 11,500 people in more than 90 countries contribute to the work of the Cochrane Collaboration. The Cochrane Collaboration has grown since its inception in 1993 in response to the need for systematic reviews of all healthcare interventions. The main work of the Cochrane Collaboration is performed by 52 Cochrane Review Groups, who prepare, maintain, and disseminate Cochrane reviews in their subject areas. The members of these Groups—researchers, healthcare professionals, people using the healthcare services (consumers), and others—have come together because they share an interest in generating reliable, up-to-date evidence relevant to the prevention, treatment, and rehabilitation of particular health problems or groups of problems. The review groups also maintain and make available to investigators specialized registers of all relevant randomized trials in their specific domains. The Cochrane Collaboration and its output have grown rapidly since the organization was established in 1993 (see Fig. 1). The first issue of the Cochrane Database of Systematic Reviews (CDSR), the main product of the collaboration, was published at the beginning of 1995, and included 36 Cochrane reviews. There were 500 Cochrane reviews in 1999, and as of Issue 3, 2010 the CDSR now contains 4186 Cochrane reviews, each of which will be kept up to date as new evidence accumulates. Issue 3, 2010 also contains 1924 published protocols for reviews in progress. These protocols set out how each review will be done and provide an explicit description of its objectives and the methods to be used. Hundreds of newly completed reviews and protocols are added to the CDSR each year. In addition, existing reviews are updated as new information becomes available, some so substantively that they can be considered the equivalent of new reviews. Cochrane Database of Systematic Reviews Issue 1, 1995 to Issue 4, 2009. Cochrane systematic reviews are published in the Cochrane Library, an electronic database of systematic reviews that is currently available free of charge to half the world's population, about 3 billion people. Countries with free access for all citizens include the United Kingdom, Ireland, the countries of Scandinavia, New Zealand, Australia, India, South Africa, Spain, and Poland. In the United States free access is available in the state of Wyoming. In Canada, the Cochrane Library is available free of charge to all residents of New Brunswick, Nova Scotia, Saskatchewan, North West Territories, Nunavut, and the Yukon. Many people in other Canadian provinces gain access via university and hospital libraries. There are also arrangements for free access in much of Latin America and in “low-income” countries. Wiley InterScience and the Cochrane Collaboration Website make abstracts and consumer synopses of all Cochrane systematic reviews freely available without subscription (http://www2.cochrane.org/reviews/en/topics/73_reviews.html). The use of the Cochrane Library has grown considerably over the past few years. For example, usage for 2009 grew by 19% compared to 2008 for full-text downloads from the Cochrane Library on Wiley InterScience. In 2009 there were 3.7 million full-text Cochrane reviews and 4.8 million abstracts downloaded from the Cochrane Library. When considering usage across all Web platforms (including Wiley InterScience, Cochrane.org, La Bibliotheca Cochrane Plus, Bireme, OVID, and EBSCO) it has been estimated that there was a search on the Cochrane Library every 1 second, an abstract viewed every 2 seconds and a full-text review downloaded every 3 seconds in 2009. The Cochrane IBD/FBD review group prepares systematic reviews of healthcare interventions directed at ulcerative colitis, Crohn's disease, and functional bowel disorders. The IBD/FBD review group has over 320 members worldwide including 270 authors, 8 editors, 43 peer reviewers, and 6 consumers. As of Issue 4, 2010 (publication date April 14, 2010) the IBD/FBD review group will have 54 systematic reviews and 30 protocols published in the Cochrane Library. The systematic review on omega 3 fatty acids for maintenance of remission in inflammatory bowel disease published in this issue of Inflammatory Bowel Diseases is based on two Cochrane reviews: 1) Omega 3 fatty acids (fish oil) for maintenance of remission in Crohn's disease; and 2) Omega 3 fatty acids (fish oil) for maintenance of remission in ulcerative colitis. In an effort to bridge the gap that exists between care that is consistent with current evidence, and that which is actually provided to patients, the IBD journal plans to publish up to four Cochrane reviews on topics of interest to the practicing clinician and IBD patients per year.

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