To understand the answers to these two questions, one must first understand the power of the randomized controlled trial (RCT) in clinical research. Although several RCTs had been conducted and reported over the centuries, full adoption of this study design didn’t occur until the 20th century.
Traditionally, evaluation of the effectiveness of a therapy was conducted by allocating one group of patients to the intervention in question and another to the standard of care or placebo. The allocation process was often biased (although not necessarily intentionally) such that one group would have a better or worse prognosis than the comparator group at the start of the trial before they even received the intervention in question. This, of course, led to unreliable results. Following the publication of landmark RCTs in the first half of the century, more and more physicians and scientists began to appreciate how randomization balanced the distribution of unknown prognostic factors between each of the groups in a clinical trial. This balancing resulted in more reliable (and conservative) results than from non-randomized studies.
Archibald Cochrane (1909–1988), after whom the Cochrane Collaboration was named, was a British physician and researcher who earned recognition as an epidemiologist and pioneer of evidence-based medicine through his outspoken views on healthcare. In his book, Effectiveness and Efficiency: Random Reflections on Health Services, he proposed that the delivery of healthcare would be best served by applying the limited healthcare resources to those healthcare strategies that had been proven to be effective via rigorous scientific methods, in particular the RCT.
Several years later, as recognition and utilization of the RCT grew in medical research, Cochrane pointed out that the medical profession needed to organize a critical summary of RCTs categorized according to specialty. Although literature reviews and similar narratives were commonly found in the medical literature, systematic reviews were unheard of. A systematic review of RCT’s of care during pregnancy and childbirth was pronounced by Cochrane as “a real milestone in the history of randomised trials and in the evaluation of care”. He further suggested that other specialties should conduct systematic reviews using similar methods.
A systematic review is a summary of healthcare research focused on a single question. It differs from other literature reviews in that it uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies to identify, select, and summarize the evidence. When the results of these studies are combined via statistical methods to create a single measure of effectiveness, the review is called a meta-analysis. Hence all meta-analyses are systematic reviews but not all systematic reviews are necessarily meta-analyses. Given that the RCT is the most powerful clinical research design, a systematic review of RCTs is the highest level of published evidence that can be achieved.
Cochrane’s repeated calls for a medical research repository of RCTs subsequently led to the development of an international collaboration, the Oxford Database of Perinatal Trials and later the first Cochrane centre (Oxford, 1992) and the Cochrane Collaboration (1993). The Cochrane Collaboration (www.cochrane.org) currently consists of 15 Cochrane Centres worldwide with over 11,500 volunteers in more than 90 countries. These people are divided into 51 Review Groups committed to developing and maintaining systematic reviews relevant to a particular health area. Unfortunately there is no Emergency Medicine Cochrane Review Group yet. What makes Cochrane systematic reviews so valuable and highly regarded is the high methodological standards that are consistently applied to create each review. That’s not to say that every completed Cochrane Review is infallible. The results of any systematic review are only as valid as those of the primary studies selected.
Archie Cochrane was a visionary advocate of quality medical care. His actions led to the creation of a worldwide collaboration of physicians and scientists working to maintain a database of the highest quality medical information for the rest of us.
Andrew Worster, MD, is an associate professor and chair of the BEEM Course at McMaster University