HR = Probability of event in treatment grp/Probability of event in control group
RR = Probability of event in treatment grp/Probability of event in control group
Exactly! same formular!
Hazard ratio is actually a type of Relative risk (a.k.a Risk ratio)
HR is instantaneous while RR is culmulative.
RR can only be calculated at the end of the study while HR can be calculated at different points in time. Hazard ratios are calculated using the survival analysis technique. This keeps track of the number of subjects who haven't had the event (e.g death) at a particular time.
Again, HR is an estimate of RR
HR of 1 means the rate of occurrence of the event in treatment/intervention grp is same as in control/placebo grp
HR >1 means event occurs more in the intervention grp
HR <1 means event occurs less in the intervention grp
To convert a HR to probability,
Probability of event occurring = HR/1+ HR
So, HR of 1 is a probability of 50%. A 50:50 chance, i.e treatment and placebo grps are the same in terms of outcome