1. What is Relative Risk?

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

2. How Does the Calculator Work?

The calculator uses the Relative Risk formula:

Where:

• \( a \) — Number of exposed cases
• \( b \) — Number of exposed non-cases
• \( c \) — Number of unexposed cases
• \( d \) — Number of unexposed non-cases

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

3. Interpretation of Relative Risk

Details:

• RR = 1: No association between exposure and outcome
• RR > 1: Increased risk in exposed group
• RR < 1: Decreased risk in exposed group (protective effect)

4. Using the Calculator

Tips: Enter all four values from your 2×2 contingency table. All values must be non-negative integers, and denominators (a+b) and (c+d) must be greater than zero.

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 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 RR?
A: RR can overestimate effect size for common outcomes. It's also sensitive to baseline risk in the population.

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