The catalogue of bias

Biases may arise in any stage of healthcare research and are likely to influence the magnitude and direction of the results.1 Understanding where and how different biases emerge in the research process allows researchers to properly design studies that can prevent or counteract the impact of biases. Furthermore, to assess the risk of bias within published studies is imperative when drafting any research synthesis and clinical practical guidelines.

Sackett, in a remarkable paper published in 1979, ‘Bias in Analytic Research’, was the first to propose a catalogue that would include a list of biases that ‘may distort the design, execution, analysis and interpretation of research’.1 2 Sacket’s pioneering work identified, labelled and discussed 35 biases. In the conclusion of this paper, Sackett highlighted, among others, two priorities for future researches: the continued development of the proposed catalogue and the empirical evaluation of the proposed biases.2

Forty years after Sackett’s paper, a group of researchers from the University of Oxford’s Centre for Evidence-Based Medicine (CEBM) decided to continue Sackett’s mission by creating an expansion to his original catalogue of bias.1 Fifty-two biases have been catalogued and discussed so far. All the content related to each bias is freely available at the official catalogue’s website (https://catalogofbias.org), including any new biases that may be catalogued after the publication of this article.

Although Sackett had little empirical evidence on the proposed original biases, the development of systematic methodologies for identifying biases and …