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good explanations by Ted and Jo...some more... Hazard ratios are commonly used when presenting results inclinical trials involving survival data, and allow hypothesistesting. They should not be considered the same as relativerisk ratios. When hazard ratios are used in survival analysis, this may havenothing to do with dying or prolonging life, but reflects theanalysis of time survived to an event (the event may, insome instances, include cure). A hazard is the rate at which events happen, so that theprobability of an event happening in a short time interval is thelength of time multiplied by the hazard. Although the hazardmay vary with time, the assumption in proportional hazardmodels for survival analysis is that the hazard in one groupis a constant proportion of the hazard in the othergroup. This proportion is the hazard ratio. The hazard ratio is an expression of thehazard or chance of events occurring in thetreatment arm as a ratio of the hazard of theevents occurring in the control arm. The termhazard ratio is often used interchangeablywith the term relative risk ratio to describeresults in clinical trials. This is not strictlycorrect as there are subtle and importantdifferences. It is useful to understand themeaning of the term and also be able toidentify when it is used appropriately. Hazardratios are increasingly used to express effectsin studies comparing treatments whenstatistics which describe time-to-event orsurvival analyses are used. this is really good...I have found and used... http://www.medicine.ox.ac.uk/bandolier/painres/download/whatis/What_are_haz_ratios.pdf Best, Paul E. Alexander --- On Wed, 3/14/12, Jenny Morris <[log in to unmask]> wrote: From: Jenny Morris <[log in to unmask]> Subject: Interpretation of hazard ratios To: [log in to unmask] Received: Wednesday, March 14, 2012, 9:08 AM Can anyone give me a easy to understand definition of hazard ratios and how they should be interpreted. This is a for a group of pre-registration nursing students. Thanks. Jenny Dr Jenny MorrisAssociate Professor (Senior Lecturer) in Health StudiesFaculty of Health, Education and SocietyUniversity of PlymouthKnowledge SpaTreliskeTruro TR1 3HDCornwall Tel: 01872 256461Web: http://www.plymouth.ac.uk/faculties/health ‘High quality education for high quality care’