How to Calculate Risk Reduction

The phrase "risk reduction" is used to describe the reduction in risk someone has when a certain activity or variable is removed from the equation. As an example, a scientist may have a theory that someone can contract cancer if they work near power lines. In order to find if their thesis is correct, they would calculate the reduction of risk for someone contracting cancer who does not work near power lines versus someone who does. This information is used in clinical trials in order to determine the most effective treatment when trying to fight diseases.

Things You'll Need

• Calculator

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Instructions

• 1

  Form two groups for the experiment. One group will be the "control group," meaning they will be used as a comparison for the other group, which is the "experimental group." In the sample experiment where we are testing to see how the proximity to power lines will affect a person's likelihood to develop cancer, the two groups will consist of people who don't work near power lines (control group) and a group of people who do (experimental group). The larger the groups, the more accurate your calculation will be.

• 2

  Question the people to determine how many of the people in both the experimental group and control group have contracted cancer. If you have more questions for the group, feel free to ask them in order to get more data to draw from, but when calculating risk reduction, you can only calculate it for one variable at a time.

• 3

  Calculate the information to find the event rate. Take the amount of people who have contracted cancer (the variable) and divide it by the group they are in. For example, if 5 people have contracted cancer out of a 100 person control group, the control group event rate is 0.05. If 20 people have contracted cancer out of a 100 person experimental group, the experimental event rate is 0.2.

• 4

  Find the risk reduction. Subtract the control event rate (0.05 in our example) by the experimental event rate (0.2) to find an event rate ratio (0.15). Then divide that event rate ratio (0.15) by the original control event rate (0.05) to get the risk reduction (3).