Relative Risk Calculator

Formula

To calculate the Relative Risk (R):

$$R = \frac{a / (a + b)}{c / (c + d)}$$

Where:

R is the relative risk
a is the number of people in the exposed group with the disease
b is the number of people in the exposed group without the disease
c is the number of people in the control group with the disease
d is the number of people in the control group without the disease

What is Relative Risk?

Relative risk is a statistical measure used to assess the likelihood of an event occurring in one group compared to another. It is a ratio that compares the probability of an outcome happening in one group to the probability of the same outcome occurring in another group.

One key application of relative risk is in studying the effects of exposure to certain risk factors on the development of diseases. For example, researchers may investigate the relative risk of developing lung cancer in smokers compared to non-smokers. By calculating the relative risk, they can quantify the increased likelihood of developing lung cancer among smokers, providing valuable information for public health interventions and targeted prevention strategies.

Relative risk also plays a vital role in clinical trials and in evaluating the effectiveness of interventions or treatments. Researchers compare the relative risk of an event occurring in the treatment group to that in the control group. This analysis enables them to determine whether the intervention has a significant impact on reducing the risk of the outcome or disease.

Example Calculation 1

Let's assume the following values:

Number of people in the exposed group with the disease (a) = 50
Number of people in the exposed group without the disease (b) = 150
Number of people in the control group with the disease (c) = 30
Number of people in the control group without the disease (d) = 170

Using the formula:

$$R = \frac{50 / (50 + 150)}{30 / (30 + 170)} = \frac{50 / 200}{30 / 200} = \frac{0.25}{0.15} = 1.67$$

The Relative Risk is 1.67.

Example Calculation 2

Let's assume the following values:

Number of people in the exposed group with the disease (a) = 80
Number of people in the exposed group without the disease (b) = 120
Number of people in the control group with the disease (c) = 40
Number of people in the control group without the disease (d) = 160

Using the formula:

$$R = \frac{80 / (80 + 120)}{40 / (40 + 160)} = \frac{80 / 200}{40 / 200} = \frac{0.4}{0.2} = 2.00$$

The Relative Risk is 2.00.