MR Dictionary

As Mendelian randomization (MR) becomes more commonplace in clinical guidelines and drug development, the MR Dictionary aims to provide useful definitions and descriptions for undertaking, understanding and interpreting MR studies to a wide, inter-disciplinary audience – both those new to MR and those who are experienced in its use but who want to remain up to date.

The MR Dictionary was borne from discussions with course and conference attendees, colleagues, and collaborators, all of whom were keen to have a publically available and easy-to-use platform that provided an overview of MR theory, methodology and interpretation.


We'd like to thank Tim Frayling (University of Exeter, UK), Rachel Freathy (University of Exeter, UK), Jackie Lane (The Broad Institute, USA), Neil Pearce (London School of Hygiene & Tropical Medicine, UK), Martine Rutter (Manchester University, UK) and Jess Tyrrell (University of Exeter, UK) for their useful comments on a draft of the MR Dictionary. We thank all who were involved in these discussions.


  • Kaitlin Wade
  • Deborah Lawlor
  • Maria Carolina Borges
  • Tom Palmer
  • Fernando Pires Hartwig
  • Gibran Hemani
  • Jack Bowden.

Production Team

  • Kaitlin Wade
  • Deborah Lawlor
  • Stuart Church
  • Kieren Pitts
  • Claire Webster
  • Serena Cooper


Creation and development of the MR Dictionary was funded by the Medical Research Council (MRC), the University of Bristol, the MRC Integrative Epidemiology Unit, the NIHR Biomedical Research Centre at University Hospitals Bristol NHS Foundation Trust, the British Heart Foundation, US National Institutes of Health, European Research Council, UK National Institute of Health Research, the Wellcome Trust, the Elizabeth Blackwell Institute for Health Research and the Royal Society. For more information on the MRC Integrative Epidemiology Unit, please see our website:


For general information about Mendelian randomization (MR), please peruse the following library of videos.

A two-minute primer on Mendelian randomization
George Davey Smith on "How our genes conduct randomised trials"