1. What is Relative Risk Ratio?

Definition: Relative Risk (RR) is a measure of the strength of association between an exposure and an outcome in epidemiological studies.

Purpose: It compares the probability of an outcome occurring in an exposed group versus an unexposed group.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( RR \) — Relative Risk (dimensionless)
• \( a \) — Exposed with outcome (number of cases)
• \( b \) — Exposed without outcome (number of controls)
• \( c \) — Unexposed with outcome (number of cases)
• \( d \) — Unexposed without outcome (number of controls)

Interpretation:

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

3. Importance of Relative Risk

Details: RR helps quantify how much more (or less) likely the outcome is in people exposed to a risk factor compared to those not exposed.

4. Using the Calculator

Tips: Enter the counts for each cell in the 2×2 contingency table. All values must be ≥ 0 and denominators (a+b) and (c+d) must be > 0.

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 RR most appropriate?
A: In cohort studies and randomized controlled trials where true probabilities can be calculated.

Q3: How do I interpret an RR of 2.5?
A: The exposed group has 2.5 times the risk of the outcome compared to the unexposed group.

Q4: What are the limitations of RR?
A: RR doesn't indicate absolute risk and can be misleading when baseline risks are small.

Q5: How precise is the RR calculation?
A: Precision depends on sample size. Consider calculating confidence intervals for more complete interpretation.