Calculate Relative Risk In Epidemiology

Relative risk is also known as the risk ratio and is not difficult to calculate if two values are known. The two values are the incidence rates for people with a known (or suspected) risk factor and the incidence for people without the risk factor.

Instructions

1. Calculate the incidence rates. These rates are like most percentages because they are the "part over the whole." This means that they are a fraction with a smaller number over a larger number. The larger number represents the entire population, while the smaller number is a section of the population. The number of people in a section of the population divided by the number of people in the entire population creates a number that is known as an incidence rate and is used to calculate the risk of getting a disease.

2. Understand the incidence rate for someone getting a certain disease in a given population with a specific risk factor is calculated by dividing the number of people sick who have that risk factor by the total number of people in the population.

3. Realize the incidence rate for someone (not singled out based on a risk factor) getting a certain disease in a given population is calculated by dividing the number of people sick by the total number of people in a given population.

4. Know that the relative risk is calculated by dividing the incidence rates by each other. With the incidence rate of a given sickness from people who have a certain risk factor (Step 2) divided by the incidence rate of people without the risk factor (Step 3), the resulting number is the relative risk which tells the likelihood of someone getting a disease based on the risk factor when compared to people in the general population.

5. Recognize that if the relative risk number is at (or nearly at) 1, it means that there is no real difference between the two groups. As the number increases above 1, the number indicates how much more likely a person is to get sick with a given risk factor with the number being how many times more likely they are to get sick if they have the risk factor. If the relative risk number is below 1, it shows a decrease in likelihood of getting sick.

Tags: risk factor, number people, incidence rate, calculated dividing, given population, incidence rates