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 is Relative Risk Calculated?

The formula for relative risk is:

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 compares the event rate in the treatment group to the event rate in the control group. An RR of 1 means no difference between groups.

3. Interpretation of Relative Risk

Details:

• RR = 1: No difference between groups
• RR > 1: Increased risk in treatment group
• RR < 1: Decreased risk in treatment group (potential protective effect)

4. Using the Calculator

Tips: Enter the number of events and total subjects for both treatment and control groups. All values must be non-negative integers.

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 is relative risk most appropriate?
A: RR is ideal for cohort studies and randomized controlled trials where true probabilities can be calculated.

Q3: How precise is relative risk?
A: Precision depends on sample size. Confidence intervals should always be reported with RR.

Q4: Can RR be greater than 1?
A: Yes, RR > 1 indicates increased risk in the treatment/exposed group.

Q5: What does RR = 0.5 mean?
A: The treatment group has half the risk of the outcome compared to the control group.