The Cochrane Library
11 April 2008
In 1972 Archie Cochrane, a British epidemiologist, drew attention to the medical profession's ignorance about the effects of health care. Those who want to make informed decisions about treatments, he pointed out, did not have access to reliable reviews of the available evidence. Such reviews need to be prepared systematically and kept up-to-date to take account of new evidence. This affects not only the practice of health care but also plans for new research.
The Cochrane Collaboration
The Cochrane Collaboration was set up in response to Cochrane's call for systematic reviews of all relevant randomised control trials (RCTs). The first Cochrane Centre opened in Oxford in October 1992 and was the result of the work of the NHS Research and Development Programme. In October 1993, at the first annual Cochrane Colloquium, 77 people from 11 countries co-founded the Cochrane Collaboration.
This is now a large international network involving 4000 people who work largely on a voluntary basis. The Collaboration produces and updates systematic reviews on the basis of hand searching the literature for RCTs. It has a strict methodology which informs the work on the Cochrane Library:
Go to the website here http://www.cochrane.org/
The Cochrane Library is a manifestation of the current interest in evidence based medicine (EBM). This has been defined by Sackett (one of its most important advocates) as the "use of current best evidence in making decisions about the care of individual patients".
Two ideas underpin EBM:
- there is too much specialist information for a general physician to sort out
- the most useful information many current practices in medicine are not supported by properly designed statistical research
The Cochrane Library does not have information on current research or statistical information. Moreover some medical specialties, such as emergency medicine, are unsuited to randomised controlled trials as all patients have to be treated. For information on diagnosis, prognosis, epidemiology it is often more appropriate to use Medline.
The main focus of EBM and Cochrane Library is that only randomised controlled trials constitute the best evidence.
Some key terms are:
Randomised controlled trials: patients are assigned to one of two groups at random. One group is given the treatment being studies; the other group is given a placebo (a "drug" which has no effect) or the usual treatment. The second group acts as a control to measure the effect of the first treatment.
A systematic review combines all of the randomised controlled trials or other studies on one subject. By pooling together all of the studies, researchers can get a much larger sample.
A meta-analysis produces a numerical figure from the systematic review which is an estimate of the effectiveness of the treatment.
The Cochrane Library
The main output of the Collaboration is the Cochrane Library. It is updated quarterly and sold by annual subscription on disc, CD-ROM and via the Internet.
National provisions give free access in some circumstances: residents of England, Wales and Northern Ireland with internet access can gain access.
Go here to see national provisions http://www3.interscience.wiley.com/cgi-bin/mrwhome/106568753/AccessCochraneLibrary.html
Databases making up the Cochrane Library
The concept of levels of evidence is central to EBM and to the structure of Cochrane Library. The best type of evidence is given first.
Meta-analysis of good quality randomised controlled trials
One good quality randomised controlled trial
One well designed controlled study with some randomisation
One well designed controlled study without randomisation
This is reflected in the Cochrane Library's different databases:
- The Cochrane Database of Systematic Reviews (CDSR) This is a rapidly growing collection of regularly updated, systematics reviews of the effects of health care. New reviews are added with each issue. The reviews are mainly of RCTs. Evidence is included on the basis of explicit quality criteria to minimise bias. Data are always combined statistically to produce meta-analysis thus incorporating studies which are too small to produce reliable results individually. The main purpose is to provide more reliable evidence on which to base clinical decisions.
- Database of Abstracts of Reviews of Effectiveness (DARE) DARE includes structured abstracts of systematic reviews from around the world which have been critically appraised by reviewers at the NHS Centre for Review and Dissemination at the University of York
- The Cochrane Controlled Trials Register (CCTR) CCTR is a bibliography of controlled trials identified by contributors. The database includes reports published in conference proceedings and in many sources not currently listed in Medline or other bibliographic databases.
- The Cochrane Review Methodology Database
- The Cochrane Review Methodology Database Handbook on Critical Appraisal - discusses how to carry out a systematic review
- Glossary of methodological terms
- Contact details of the Collaborative Review Groups
Advantages of Cochrane Library include:
- The specialists who produce the systematic reviews use standard databases like Medline or Embase but also search journals by hand or talk to experts to find unpublished or unindexed studies.
- The reviews are scientific rather than individual or subject summaries of available information.
- The reviews summarise perhaps thousands of research papers in 20 or 30 pages. The subjects are topical areas which doctors have to make decisions: does hypnotherapy help people stop smoking?; do certain types of mattress stop pressure sores?