# Relative Risk

Tags:
relative risk
risk ratio
rr
probability
outcome

Science Strategy

Relative risk is a concept is useful for determining the effectiveness of a drug or medical device in reducing the risk of certain outcomes, such as hospitalizations or early death. To calculate relative risk, divide the risk in the treatment (intervention) group by the risk in the control group. The risks in each group are determined by dividing the number of participants with the outcome by the total number of participants in the group.

Using a 2x2 table, we can further analyze data with the intervention group going into A (number of people who experienced the outcome) and B (number that did not), and the control group going into C (number who experienced the outcome) and D (number that did not). With this information, calculating the Relative Risk Reduction (RRR) and Absolute Risk Reduction (ARR) becomes possible. RRR is the relative decrease in the risk of the outcome occurring in the intervention group compared to the control group, whereas ARR considers the background risk of the outcome and accounts for its absolute difference. This gives a more accurate metric when comparing risk reduction between different interventions.

Lesson Outline

<ul> <li>Relative Risk</li> <ul> <li>The probability of an outcome occurring in one group compared to another (usually a treatment group and a control group who receives no treatment)</li> <li>Useful for determining the effectiveness of a drug or medical device</li> <li>Calculation: divide the risk in the treatment (intervention) group by the risk in the control group</li> <li>Risk in each group: divide the number of participants with the outcome by the total number of participants</li> </ul> <li>Using a 2x2 table</li> <ul> <li>Four cells in the table: A, B, C, and D</li> <li>Intervention group: A (number of people who experienced the outcome) and B (number that did not)</li> <li>Control group: C (number who experienced the outcome) and D (number that did not)</li> </ul> <li>Relative Risk Reduction (RRR)</li> <ul> <li>Relative decrease in the risk of the outcome occurring in the intervention group compared to the control group</li> </ul> <li>Absolute Risk Reduction (ARR)</li> <ul> <li>Considers the background risk of the outcome</li> <li>Accounts for the absolute difference in risk</li> <li>Provides a more accurate metric when comparing risk reduction between different interventions</li> </ul> </ul> Don't stop here!

Get access to 19 more MCAT Science Strategy lessons & 8 more full MCAT courses with one subscription!

FAQs

## What is the difference between relative risk and absolute risk?

Relative risk (RR) is a comparison of the risk of an event happening in an intervention group compared to the risk in a control group. It is the ratio of the probabilities of the event occurring in the two groups, giving a sense of how much an intervention may alter the risk. Absolute risk, on the other hand, refers to the actual probability of an event occurring in a specific group, without comparing it to any other group. Understanding both relative and absolute risk is crucial for interpreting the results of clinical studies and making informed medical decisions.

## How do you calculate relative risk reduction (RRR) and what does it represent?

Relative risk reduction (RRR) is calculated by finding the difference in risk between the control group and the intervention group, then dividing that by the risk in the control group. In other words, RRR = (Risk in control group - Risk in intervention group) / Risk in control group. It represents the proportion of risk that is reduced in the intervention group compared to the control group and is typically expressed as a percentage. RRR provides valuable insight into the effectiveness of a medical intervention.

## What is the importance of absolute risk reduction (ARR) in evaluating trial outcomes?

Absolute risk reduction (ARR) represents the difference in risk between the intervention and control groups, without considering the ratio between them. It is calculated as ARR = Risk in control group - Risk in intervention group. ARR is important in assessing trial outcomes because it indicates the actual reduction in risk due to the intervention being studied. It helps clinicians and researchers determine the practical utility of a treatment or medical device by highlighting the direct risk reduction for patients receiving the intervention.

## How do you interpret and apply relative risk in the context of a medical device trial?

In a medical device trial, relative risk (RR) serves as a metric for comparing the probability of a specific event (like a health outcome or adverse effect) between the intervention group, which uses the medical device, and the control group, which does not. To interpret and apply RR, first calculate the ratio of the probabilities in both groups. An RR greater than 1 indicates the event is more likely in the intervention group, while an RR less than 1 suggests the event is less likely. An RR equal to 1 suggests no difference between groups. In context, this can help guide decisions on the effectiveness and safety of the medical device being studied, particularly in comparison to existing interventions or no intervention at all.