1. What is Relative Risk?

Relative Risk (RR) is a measure of the strength of association between an exposure and an outcome. It compares the probability of an event occurring in the treatment group versus the control group.

2. How Does the Calculator Work?

The calculator uses the Relative Risk formula:

Where:

• \( event_{treatment} \) — Number of events in treatment group
• \( n_{treatment} \) — Total number in treatment group
• \( event_{control} \) — Number of events in control group
• \( n_{control} \) — Total number in control group

Explanation: RR = 1 means no difference between groups. RR > 1 means increased risk in treatment group. RR < 1 means decreased risk in treatment group.

3. Interpretation of Results

Details:

• RR = 1: No association between treatment and outcome
• RR > 1: Treatment group has higher risk than control
• RR < 1: Treatment group has lower risk than control (protective effect)

4. Using the Calculator

Tips: Enter whole numbers for all fields. Treatment events must be ≤ treatment group size. Control events must be ≤ control group size.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between RR and odds ratio?
A: RR compares probabilities directly, while odds ratio compares odds. RR is more intuitive but can't be used in case-control studies.

Q2: When should I use relative risk?
A: RR is ideal for cohort studies and randomized controlled trials where you can calculate true probabilities.

Q3: How precise is relative risk?
A: Always calculate confidence intervals to understand the precision of your RR estimate.

Q4: What if my control group has zero events?
A: RR becomes undefined (division by zero). Consider using odds ratio instead.

Q5: How do I interpret an RR of 2.5?
A: The treatment group has 2.5 times the risk of the outcome compared to the control group.