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Recent rapid responses
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Displaying 1-2 out of 2 published
2 November 2011
I read with interest the article on the Cochrane Collaboration's tool for assessing risk of bias by Higgins et al. I am an academic foundation year two doctor working with a Cochrane review group based at the University of York. My role within the team has been to help update Cochrane reviews, adding new studies identified since the review was last published, and to make sure the review meets the current Cochrane Collaboration standards. One of the main aspects of this role was to complete the new risk of bias assessment for all the studies in the review update comprising those included before the development of the new tool. The following is a brief summary of my experiences of assessing risk of bias using the Cochrane Collaboration tool.
Initially, the task of updating Cochrane reviews was a daunting one and I had a lot to learn. I found the Cochrane Handbook1 very helpful and was well supported by the excellent team at the editorial base. For me, the main positive aspect of the risk of bias tool is its ease of use and transparency. The Cochrane Handbook1 gives very clear instructions on how to use the tool and within RevMan (Cochrane's software package) the risk of bias tables are generated and summary figures produced automatically. The process of completing the risk of bias tables is also straightforward, as every decision made by the review authors must be supported by a quote from the study text. This requirement makes the decision making process transparent and allows the reader of the review to see how the judgement of bias was supported. Finally, the summary diagrams give a clear overview of, not only each individual study's risk of bias, but of the review as a whole.
I feel I have learnt a great deal in my short time working with the review group. I quickly learnt about the different types of bias, why they are important and how to detect them within the included studies of a Cochrane review. I have acquired a valuable skill, now being able to thoroughly appraise studies and assess their potential biases. I have a better understanding of how studies should be designed and importantly what information authors should report in the study publication to enable readers to detect any potential biases and be able to form a judgement on the evidence presented. I feel these skills are essential for all doctors in order to assess the medical literature upon which their clinical decision making is based.
1. Higgins JPT, Green S, eds. Cochrane handbook for systematic reviews of interventions. Wiley, 2008.
Competing interests: None declared
University of York
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31 October 2011
To the Editor: Randomised controlled trials (RCTs) are considered to be the gold standard of clinical research and the building blocks of most systematic reviews and practice guidelines. Yet, the recently published recommended criteria for assessing risk of bias in RCTs by the Cochrane Collaboration are almost exclusively concerned with internal validity.<1> Although the recommended standards are both timely and welcomed, the perennial problem with poor uptake of clinical practice guidelines, especially in primary care settings, is an on-going neglect of the external validity or applicability in the design and conduct of randomized controlled trials (RCTs). Some of the frequently identified threats to external validity include narrow inclusion criteria, use of run -in periods, and length of follow-up or clinical relevance of the primary end-points used. <2,3,4>
Although, as stated by the authors, applicability is less relevant without internal validity, the opposite is equally true. It is disappointing to see that the external validity, once gain, was placed on the back burner. Internal and external validity are equally important, and both ought to be maximized in order to generate the evidence that is both valid and applicable. This is not a zero-sum game.
1. Higgins JPT, Altman DG, Peter C G?tzsche PC, et al. The Cochrane Collaboration's tool for assessing risk of bias in randomised trials. BMJ 343:d5928. 2011
2. Fortin M, Dionne J, Pinho G, Gignac J, Almirall J, Lapointe L. Randomized controlled trials: do they have external validity for patients with multiple comorbidities? Ann Fam Med 4 104-8. 2006.
3. Rothwell PM. External validity of randomised controlled trials: "To whom do the results of this trial apply?" Lancet 365 82-93. 2005.
4. Glasgow RE, Lichtenstein E, Marcus AC. Why don't we see more translation of health promotion research to practice? Rethinking the efficacy-to-effectiveness transition. Am J Public Health 93, 1261-1267. 2003.
Competing interests: None declared
University of Montreal
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