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| good explanations by Ted and Jo...some more... 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. The hazard ratio is an expression of the hazard or chance of events occurring in the treatment arm as a ratio of the hazard of the events occurring in the control arm. The term hazard ratio is often used interchangeably with the term relative risk ratio to describe results in clinical trials. This is not strictly correct as there are subtle and important differences. It is useful to understand the meaning of
the term and also be able to identify when it is used appropriately. Hazard ratios are increasingly used to express effects in studies comparing treatments when statistics which describe time-to-event or survival analyses are 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:
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