Just like any library, the Cochrane Library is a collection of resources. It is the main output of the Cochrane Collaboration and aims to bring together in one place reliable information about the effects of health care treatments or interventions.
In the Cochrane Library health care is broadly defined, so in addition to many hundreds of medical conditions, youll find information on such diverse topics as injury prevention for pedestrians and cyclists, St Johns wort for depression, programs to reduce juvenile delinquency, the prevention of jet lag, advice on low-fat diets for obesity, and prayer for the alleviation of ill health.
The Cochrane Library is designed to ensure that evidence of effectiveness is given consideration alongside other aspects of the decision-making process, namely the expertise of the practitioner, the preferences and values of the patient, and the availability of resources. Consequently, how the evidence is interpreted and implemented needs to take account of individual circumstances. The Cochrane Library is not intended to replace consultations between practitioners and consumers.
Why do we need the Cochrane Library?
Clinicians are overloaded with information, whether in the form of research reported in journals, mailings from professional groups, policy announcements from government, or promotional literature from pharmaceutical companies.
To take research as just one example of information overload: over 2 million articles are published annually in some 20,000 biomedical journals equivalent to a pile of paper 500m high (or nearly two Eiffel Towers)! Its estimated that the average general practitioner needs to read 19 articles a day just to keep up-to-date with major developments. Yet we know that most health practitioners are only able to spend up to an hour a week reading the professional literature. Clearly, keeping up-to-date with all the evidence is not a task we can expect clinicians to do on their own.
Consumers too are subject to the explosion in health information - the internet, television current affairs programs, newspapers, lifestyle magazines, and advertising posters are all outlets for information about health. The provision of reliable information through the Cochrane Library can help patients and their carers to weigh up potential benefits and harms of treatment. A useful starting point for anyone unfamiliar with health research is the information assembled on the web sites of the Cochrane Consumer Network and Informed Health Online.
The Cochrane Collaboration - the international organisation that oversees the preparation of the Cochrane Library - started up in 1993 in response to Archie Cochrane's call for systematic, up-to-date reviews in health care. Cochrane was a medical researcher who 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 that because resources are always limited, its all the more important to know which interventions work. Archie Cochrane died in 1988, but the challenge he laid down to the medical profession has been taken up by the organisation that bears his name the Cochrane Collaboration.
What is the idea behind Cochrane reviews?
Much of the information in the Cochrane Library is presented in the form of systematic reviews (also referred to as Cochrane reviews). The idea behind these reviews is simple. Imagine youve come across the results of a single clinical trial of a new cream to treat eczema. The results look promising people in the group given the new cream seem to do better than the control group but the trial is very small, just twelve people. How do we know if the results from this small study would be repeated if we tested the cream in a different set of people?
The answer is we dont know for sure. So that we can conclude whether one treatment is better or more effective than another, we either need to carry out very large trials (which can be expensive and time-consuming), or we need to find all the trials that have been done around the world looking at the same intervention (in this case, the new eczema cream) and try to work out the average result from the trials. By combining lots of individual studies, reviews can provide us with conclusive evidence of the effects of health care interventions.
Opinion polls and systematic reviews.
Cochrane reviews address clearly formulated questions, for example, Can antibiotics help in alleviating the symptoms of sore throat? They are called systematic reviews because of the comprehensive and explicit methods used to track down, select and determine the quality of relevant research. In most cases, research included in Cochrane reviews comes from randomised controlled trials (RCTs). Data from studies included in the reviews are often analysed using statistical methods (meta-analysis).
Can antibiotics help in alleviating the symptoms of a sore throat?
In producing these summaries of the evidence, review authors are careful to avoid giving explicit recommendations for practice. Reviews are written for an international readership and local circumstances are likely to vary from country to country (and even within countries). Instead, review authors discuss in general terms the implications for practice, as well as the implications for future research. Wherever possible Cochrane reviews also include information on side effects or adverse reactions if this has been reported in the included studies.
The Guide includes a more detailed look at a Cochrane review.
The Cochrane Library is updated four times a year and currently contains over 3500 Cochrane reviews. About 300 new reviews are added each year. Reviews are also kept up-to-date to take account of new information. However, its unlikely that youll find answers to all your questions yet. The Cochrane Library is still a relatively new publication - it was first published in 1996 - and probably another 7,000 reviews are needed before a substantial proportion of all health care questions are covered.
If there isnt a Cochrane review on your topic then the other databases in the Cochrane Library will tell you whether other good quality reviews or randomised trials have been done. Its also worth noting that even when you do find a relevant Cochrane review, the evidence may not be conclusive. Reviews typically contain five or six studies and often this isnt sufficient to detect clear differences between treatments. Some reviews dont contain any studies. This is still an important finding as it highlights gaps in our knowledge and points out areas where scarce research funds may be put to best use.
Since the focus of the Cochrane Library is about providing information about treatment (is one intervention more effective than another) and prevention (how do we reduce the risk of this disease), you wont find reviews that consider diagnosis (what is the best test to use and how can we trust it), aetiology (the causes of a condition), or prognosis (the likely outcome, course or natural progression of a condition), although review authors may refer to these aspects in the background section of the review.
However, in the area of diagnosis things are about to change as the first reviews of diagnostic test accuracy begin to appear in the Cochrane Library. Researchers within the Collaboration are currently developing the methods and computer applications necessary to prepare and publish diagnostic reviews.
How reliable are the reviews?
Because of the rigour applied to the preparation of Cochrane reviews, they are increasingly being used to influence both policy and practice internationally. For example, they are often used as the basis for recommendations made by professional organisations when developing evidence-based practice guidelines. Cochrane reviewers go to great lengths to track down relevant studies (including those not published in regular biomedical journals), irrespective of the language the study is published in, with the aim of providing us with the best possible summary of what is currently known about the effectiveness of a particular intervention.
Cochrane reviews also follow strict criteria about the sort of studies which are eligible for review. We know that randomised trials are the most rigorous way of comparing treatments or interventions, and so most Cochrane reviews only consider evidence from this type of study. In cases where its not possible to conduct randomised trials or where no randomised trials exist, then other study types may be sought and reviewed. The aim is to minimise bias in reviews by only including studies of a certain quality.
Who does the work?
The Cochrane Collaboration is supported by hundreds of organisations from around the world, including health service providers, research funding agencies, departments of health, international organisations, industry and universities.
Over 15,000 health professionals, researchers, scientists and consumers from 100 countries contribute to the work of the Cochrane Collaboration. People interested in finding out about the effectiveness of a particular intervention form a review team to assess the available evidence. They are supported in this task by one of 52 review groups based around the world. These groups typically focus on a particular condition or group of conditions, such as the Tobacco Addiction Group or the Acute Respiratory Infections Group. These groups provide specialist help and ensure that the reviews meet the high standards required for publication in the Cochrane Library.
Australia is one of the most active countries within the Cochrane Collaboration with over 1000 review authors. Australia also has a strong tradition of consumer involvement in health, and many consumers contribute to the preparation of reviews. Consumer reviewers come from a variety of backgrounds and have often developed an interest in health research through participation with local consumer organisations. Consumer involvement in the review process helps to ensure that the questions review authors attempt to answer are relevant to people with the condition or their carers. Further information about how consumers contribute to the work of the Cochrane Collaboration can be found on the Cochrane Consumer Network website.
Who pays for it?
Most Cochrane review authors volunteer their time to write reviews. Clinicians and researchers involved in reviews tend to be employed in the university or hospital sectors. Consumer reviewers also contribute on a voluntary basis. The many groups that make up the Cochrane Collaboration are predominantly funded from public sources, usually by national departments of health. In keeping with the Collaborations aim of preparing reviews that are as systematic and as free from bias as possible, there are strict guidelines for avoiding potential financial conflicts of interest. The Collaborations policy on commercial sponsorship was revised in April 2004 and is available on the Cochrane website.
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