Better late than never:


“Looking back, one thing that would have been especially useful is a list of key biases in health research, with real-world examples, as well as  their potential impact and how this affects interpretation and use of evidence in health care decision making.”

David Nunan

Better late than never: A Catalogue of the biases affecting health research

My first introduction to evidence-based medicine (EBM) was when I joined the Centre for Evidence-Based Medicine (CEBM) 8 years ago. Shortly after I arrived, I attended a CEBM one-day workshop on EBM. That was it–I was hooked. I had to get into this. I still am, and loving every bit of it, especially teaching (and, I hope, inspiring) others.

As a teacher, I must have taught between 500 and 1000 learners the basics (and not-so-basics) of EBM. Looking back, one thing that would have been especially useful is a list of key biases in health research, with real-world examples, as well as their impact and how this affects interpretation and use of evidence in health care decision making. Oh, and steps to prevent them would be nice too. Not asking for much then.

You know what they say about ideas – there’s a good chance someone else has already thought of it. Well, that’s exactly the case here. A 1979 paper entitled “Bias in Analytic Research”, published in the Journal of Chronic Diseases, by David Sackett reported the first draft of a ‘catalog of biases which may distort the design, execution, analysis and interpretation of research.’ Sackett catalogued 35 biases that arise in sampling and measurement, in the context of clinical trials, and listed 56 biases potentially affecting case-control and cohort studies.

He proposed the continued development of an annotated catalogue of bias as a priority for research, stating that each citation should include a useful definition, a referenced example illustrating the magnitude and direction of its effects, and a description of the appropriate preventive measures if any.

To better understand the persistent presence, diversity and impact of biases, we are compiling a Catalogue of Bias, stemming from original work by David Sackett. The entries are a work in progress and describe a wide range of biases –  outlining their potential impact in research studies.

The Catalogue of Bias Collaboration is, therefore, taking forward the task of creating a Catalogue of Bias in memory of David’s work. We welcome further contributions and collaborations in order to continually refine and update this resource.

David Nunan, on behalf of the Catalogue of Bias Collaboration.

David Nunan is a departmental lecturer and senior researcher at the Centre for Evidence-Based Medicine,  Nuffield Department of Primary Care Health Sciences, University of Oxford. He is also lead tutor of the Practice of Evidence-Based Health Care module on the MSc in Evidence-Based Health Care. You can follow him on Twitter @dnunan79

Disclaimer: The views expressed in this commentary represent the views of the authors and not necessarily those of their host institution, the NHS, the NIHR, or the Department of Health.

Declaration of interest: DN has received expenses and fees for his media work. He holds grant funding from the NIHR School of Primary Care Research and the Royal College of General Practitioners. On occasion, he receives expenses for teaching EBM.