The aim of the Cochrane Library is to prepare, maintain, and promote the accessibility of systematic reviews of the effects of healthcare interventions. It contains 4 databases: the Cochrane Database of Systematic Reviews (CDSR), the Database of Abstracts of Reviews of Effectiveness (DARE), the Cochrane Controlled Trials Register (CCTR), and the Cochrane Review Methodology Database (CRMD). They all use the same search engine.

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The Cochrane Library

The CDSR contains systematic reviews that are prepared by using explicit criteria for searching the literature and for appraising and synthesising the retrieved evidence. Evidence is included or excluded on the basis of quality criteria to minimise bias. These reviews focus on issues of treatment and thus primarily include randomised controlled trials. 47 Collaborative Review Groups are currently working on reviews. Each systematic review contains an informative abstract; detailed descriptions of the objectives, study inclusion criteria, search strategy, study methods, methodological quality of the studies, and study results; and a discussion.

DARE includes structured abstracts of systematic reviews from many sources that have been critically appraised by reviewers at the UK National Health Service Research and Development Centre for Reviews and Dissemination.

The CCTR is a database of controlled trials that have been identified by the Cochrane Collaboration in an effort to hand search the world's healthcare journals and to examine bibliographic databases (eg, Medline and EMBASE/Excerpta Medica). It includes reports published in conference proceedings and in other sources not indexed in other bibliographic databases. Several pharmaceutical manufacturers have provided the results of their unpublished studies for this register.

The CRMD contains >1000 articles on how to produce systematic reviews and meta-analyses.

I use the Cochrane Library frequently during my consultations with patients. For example, 2 weeks ago I saw a patient in my office who had Bell palsy <48 hours in duration. My question was, “What is the efficacy of steroids in such a patient?” Within 30 seconds, I was able to launch the software, which appears as an icon on my desktop, to unsuccessfully search for “Bell's,” to subsequently search using the MeSH term “facial paralysis,” and to find a review in DARE. After an additional 35 seconds, I determined 4 important facts: 77% of patients with Bell palsy who take steroids recover, 64% of patients who are prescribed placebo recover, the mean time required for patients to recover is 2 months, and the quality of the studies is not sufficiently good to date for the authors to be confident of the results. The main message I presented to my patient was that two thirds of patients with Bell palsy get better without any treatment, which was reassuring to her. I was also able to tell her that it might take ≥2 months for the paralysis to resolve and that the additional benefits of steroids are unclear. Given this information, she decided to try a course of steroid treatment. She watched and participated in the entire process of searching the Cochrane Library.

The Cochrane Library has not always been as useful to me as it was in the above scenario. Only 1388 reviews are listed in CDSR Issue 1 for 2000, and therefore, not all topics are covered. I've also found that searches of the Cochrane Library can take a long time and that you may not always be able to finish a search during your consultation. It also takes a while to become familiar with the layout of the library. Sometimes the systematic review is quite complex, and it is often difficult to find the clinical bottom line. Finally, if you are becoming familiar with numbers needed to treat (NNTs), then you will be disappointed with the Cochrane Library. No software is included that allows calculation of NNTs by using odds ratios.

Despite these minor concerns, I have used the Cochrane Library since the first issue was published and regard it as the best source for the highest quality evidence.

New editions of the Cochrane Library are prepared quarterly. New reviews are added, and existing reviews in the CDSR are modified and updated with each new version.