What is the difference between incidence rate ratio and relative risk ratio?

Answer 1

Incidence rate and relative risk are two different measurements used in epidemiology to study illness/disease in specified populations.

Incidence rate refers to the number of new cases of a condition in a defined (specified) group or population. It is often expressed as a ratio. For example, if there are 1000 people and 14 of them develop a condition, the incidence rate is 14 per 1000 or 1.4%

Relative risk is a measurement that indicates probability of cause. In other words, how likely is it that a place, person or agent is responsible for causing disease/illness.

Before you can calculate relative risk, you must first calculate an attack rate on different groups. An attack rate refers to the number of people exposed to an illness compaired to those who actually became sick. To calculate the attack rate, you divide the number of people ill by those who were exposed, and then multiply by 100.

To then calculate the relative risk, you divide the attack rate of those sick by the attack rate of those who are not sick.

The closer the relative risk is to 1.0, the less likely it is the cause of disease.

The higher the relative risk, the more likely it is that it is the cause of disease.