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So is it really just different terms, while the figures are actually the same? But RR is usually used to show a constant mean, which like linear regression is between -1 and 1 [averaged over time to appear constant] while HR is presented as a curved regression that can show changes over time in the mean survival rates between -1 to 1? Jo ________________________________ From: Paul Elias <[log in to unmask]> To: [log in to unmask]; jo kirkpatrick <[log in to unmask]> Sent: Wednesday, 14 March 2012, 15:07 Subject: Re: Interpretation of hazard ratios these questions are difficult to answer since there is so much one can talk on each...to me in the broad sense there is no difference between harzard ratio and relative risk...and I dont pretend to be the expert but its my view at this time... both are computed to compare the chance or probability of an event happening in 2 (or groups. Thus f the relative risk (RR) or hazard ratio (HR) is 1.0, then the two groups have the same chance of having whatever the study is measuring, be it sudden death or the like. The difference to me is in the method they are computed...RR is done by the ratio of 2 risks/rates or incidence of disease or outcome in the exposed over the incidence in the unexposed (a/a+b) /(c/c+d) while the harzard ratio is computed by looking at the ratio of 2 harzards based on 2 survival curves...survival analysis where 2 different groups (A vs B) are followed over time ...some argue that RR is a harzard ratio averaged over time.... Best, Paul E. Alexander --- On Wed, 3/14/12, jo kirkpatrick <[log in to unmask]> wrote: >From: jo kirkpatrick <[log in to unmask]> >Subject: Re: Interpretation of hazard ratios >To: [log in to unmask] >Received: Wednesday, March 14, 2012, 2:21 PM > > >I am having trouble finding out exactly what are these subtle but important difference between Hazard and Risk ratios, can anyone illustrate these better than the resources I have found? The Cochrane Handbook says: [if I understand it correctly] Hazard ratios are similar to relative risk/odds ratios except Hazard ratios refer to instantanious risk that may be subject to continuous change, while in the RR OR the risk remains constant. > > > >Is this about right? > > > >Jo > > > > >________________________________ > From: Paul Elias <[log in to unmask]> >To: [log in to unmask] >Sent: Wednesday, 14 March 2012, 13:20 >Subject: Re: Interpretation of hazard ratios > > >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. > >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 Morris >>Associate Professor (Senior Lecturer) in Health Studies >>Faculty of Health, Education and Society >>University of Plymouth >>Knowledge Spa >>Treliske >>Truro TR1 3HD >>Cornwall >> >>Tel: 01872 256461 >>Web: http://www.plymouth.ac.uk/faculties/health >> >>‘High quality education for high quality care’ >> >> >> > >