1. What is Risk Ratio?

The Risk Ratio (RR), also called Relative Risk, compares the probability of an outcome between two groups. It's commonly used in epidemiology to measure the strength of association between exposure and outcome.

2. How Does the Calculator Work?

The calculator uses the Risk Ratio formula:

Where:

• \( a \) — Number of exposed individuals with outcome
• \( b \) — Number of exposed individuals without outcome
• \( c \) — Number of unexposed individuals with outcome
• \( d \) — Number of unexposed individuals without outcome

Explanation: The numerator calculates the risk in the exposed group, while the denominator calculates the risk in the unexposed group.

3. Interpretation of Risk Ratio

Details:

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

4. Using the Calculator

Tips: Enter counts for each cell in the 2×2 contingency table. All values must be non-negative integers.

5. Frequently Asked Questions (FAQ)

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

Q2: When is Risk Ratio most appropriate?
A: RR is ideal for cohort studies and randomized controlled trials where true risks can be calculated.

Q3: How precise should RR values be reported?
A: Typically reported with 2 decimal places, along with confidence intervals for precision.

Q4: What are limitations of Risk Ratio?
A: RR can't be calculated when the unexposed group has zero events. It may also exaggerate small absolute differences.

Q5: How do I interpret a RR of 2.5?
A: A RR of 2.5 means the exposed group has 2.5 times the risk of the outcome compared to the unexposed group.