Martin Duerden

Sessional GP, and Clinical Senior Lecturer, Centre for Health Economics and Medicines Evaluation, Bangor University

Author of: What are hazard ratios?

Dr Martin Duerden has carried out regular sessional work as a part-time GP in Conwy, North Wales since 1999. In 2003, he became Medical Director at Conwy Local Health Board, reorganised to Betsi Cadwaladr University Health Board for North Wales in 2009, where he became Deputy Medical Director until 2014. He qualified at Newcastle University and was a full-time GP in the north east of England for eight years until 1994.

He worked for several years as Medical Adviser to East Norfolk Health Authority and subsequently trained in public health medicine in Cambridge.

For three years Dr Duerden worked as Medical Director for the National Prescribing Centre for England, based in Liverpool. Following this, from 2001 he worked on various projects: as a medicines management consultant for University College London Hospitals Trust; with the PRODIGY project on decision support for general practice; and at Keele University.

Dr Duerden is on the Editorial Board of Prescriber, on the Paediatric Formulary Committee for the BNF-C, and is a member of a NICE Technology Appraisal Committee and a Clinical Guideline Group. He organised the Diploma in Therapeutics at Cardiff University between 2005 and 2010. He was Chair of the New Medicines Group for Wales between 2007 and 2010. He was the lead author of two King’s Fund Reports; one on The quality of GP prescribing, published in August 2011; and the other on Polypharmacy and medicines optimisation, published in November 2013. He is a Clinical Adviser to the Royal College of General Practitioners on prescribing and on evidence-based medicine.

Summary: What are hazard ratios?

  • Hazard ratios are commonly used when presenting results in clinical trials involving survival data, and allow hypothesis testing. They should not be considered the same as relative risk ratios.
  • When hazard ratios are used in survival analysis, this may have nothing to do with dying or prolonging life, but reflects the analysis of time survived to an event (the event may, in some instances, include cure).
  • A hazard is the rate at which events happen, so that the probability of an event happening in a short time interval is the length of time multiplied by the hazard. Although the hazard may vary with time, the assumption in proportional hazard models for survival analysis is that the hazard in one group is a constant proportion of the hazard in the other group. This proportion is the hazard ratio.
  • When expressing the results of clinical trials, the hazard ratio conveys no information about the size of clinical effect and should be considered alongside a measure of time, usually the median time to the event under scrutiny comparing active treatment and control groups (the points at which half the subjects have experienced the event in each arm of the study).