Question

what is the difference between absolute risk and relative risk in epidemiology? and how are both calculated ?

Answer 1

Absolute Risk	Relative risk
A measure of the risk of a certain event happening	It is the measure of the certain event happening in one group when compared with the same event happening in different group.
When the medicine was being used by patient from 1 year the chances increased from 1 in 100 to 2 in 100.	The patient who was using this medicine has seen a significant improvement in health by 56%.
The absolute risk is the risk of something happening is the odds of that happening over a given period of time.	Relative risk is where you compare odds of two groups with each other
Absolute risk will tell about the actual odds happening, it does provide information about the risk.	While in relative risk it is opposite it will not provide any information about the actual risk.
Absolute risk is always calculated in percentage	Relative risk on the other hand isn’t calculated in percentage

ARC = the AR of events in the control group
ART = the AR of events in the treatment group

ARR (absolute risk reduction) = ARC – ART
RR (relative risk) = ART / ARC
RRR (relative risk reduction) = (ARC – ART) / ARC
RRR = 1 – RR
NNT (number needed to treat) = 1 / ARR