1. What is Risk Difference?

Definition: Risk Difference (RD) is the absolute difference in probabilities of an event occurring between two groups.

Purpose: It measures the absolute effect size in comparative studies, showing how much more (or less) likely an event is in one group versus another.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( RD \) — Risk Difference (dimensionless)
• \( P_1 \) — Probability of event in group 1 (0 to 1)
• \( P_2 \) — Probability of event in group 2 (0 to 1)

Explanation: A positive RD means the event is more likely in group 1, while a negative RD means it's more likely in group 2.

3. Importance of Risk Difference

Details: RD provides an intuitive measure of absolute effect that is easier to interpret than relative measures like risk ratios. It's particularly useful in clinical and epidemiological studies.

4. Using the Calculator

Tips: Enter probabilities as values between 0 and 1 (e.g., 0.25 for 25%). The calculator will compute the absolute difference between the two probabilities.

5. Frequently Asked Questions (FAQ)

Q1: How is risk difference different from relative risk?
A: RD shows absolute difference (P₁-P₂), while relative risk shows ratio (P₁/P₂). RD is better for understanding actual impact.

Q2: What does a risk difference of 0 mean?
A: An RD of 0 means there's no difference in event probabilities between the two groups.

Q3: What's considered a clinically significant RD?
A: This depends on context. In medicine, even small RDs (e.g., 0.01) can be important for common conditions.

Q4: Can RD be negative?
A: Yes, negative RD means the event is less likely in group 1 than group 2.

Q5: How should I interpret an RD of 0.15?
A: This means the event is 15 percentage points more likely in group 1 than group 2.