Bias enters health studies at all stages and often influences the magnitude and direction of results. To obtain the least biased information, researchers must acknowledge the potential presence of biases and take steps to avoid and minimise their effects. Equally, in assessing the results of studies, we must be aware of the different types of biases, their potential impact and how this affects interpretation and use of evidence in healthcare decision making.

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.

Sackett recognised the importance of bias in research. His 1979 paper “Bias in Analytic Research”, published in the Journal of Chronic Diseases, 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.

Sackett DL. Bias in Analytical Research. Chron Dis 1979;32:51-63

He stated 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.

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

Catalogue of Bias Collaboration: 

The Collaboration meets regularly to develop and refine the contents of the Catalogue and in between work on updating content.


Editors: Badenoch D, Heneghan C, Nunan D.

Associate Editors and authors: Aronson JKA1, Badenoch D2, Banerjee A, 3 Bankhead C, 1 Brassey JA, 4, Chalmers I, 1  Davis R, 1 Friedemann-Smith C,1  Heneghan C, 1 Lach J, 1 Mahtani K, 1 McCall M, 1 McFadden E, Nunan D,   O’Sullivan J, 1 Onakpoya I, 1  Pluddemann A, 1 Richards G, 1 Spencer EA. 1

Digital Communication Editor: Crouch A. 1

Correspondence to: carl.heneghan@phc.ox.ac.uk

1 Centre for Evidence-Based Medicine, Nuffield Department of Primary Care Health Sciences, University of Oxford

2 Minervation Ltd. www.minervation.com

3 Institute of Health Informatics, Faculty of Pop Health Sciences, University College London.

4 Trip Database Ltd.


The Catalogue of Bias would not have been possible without the funding from the McCall MacBain Foundation, which supported the development of the Catalogue of Bias. Part of the  2019 meeting was funded by a NIHR Senior Investigator award to Carl Heneghan.