What is the difference between hazard ratio and relative risk?

Question

What is the difference between hazard ratio and relative risk?

Answer 1

Both are used to compare the chance of an event happening in two (or more) groups.  So if the relative risk (RR) or hazard ratio (HR) is 1.0, the two groups have the same chance of having whatever the study is measuring, be it an heart attack or stroke or death or whatever.  In that sense, you can think of HR as an estimate of RR:

http://en.wikipedia.org/wiki/Hazard_rati...

They differ in how they are generated.  

RR is often calculated by simply divide two risks (which are in turn, calculated by dividing the people with events by the total): http://www.cchealth.org/health_data/hosp...

You can do this with a calculator from the dollar store.

On the other hand, hazard ratio is used often in the context of survival analysis, where two groups are followed over time, and the two curves are plotted.  You need fancy stats software to calculate the HR.

In that sense, you can think of HR as the RR-averaged-over-time.

Hope this doesn't confuse you more.