1. What is Risk Reduction?

Risk Reduction (RR) is the absolute difference in event rates between control and treatment groups. It measures how much a treatment reduces the risk of an event compared to the control.

2. How Does the Calculator Work?

The calculator uses the simple formula:

Where:

• \( RR \) — Risk Reduction (unitless)
• \( E_c \) — Event rate in control group (0 to 1)
• \( E_t \) — Event rate in treatment group (0 to 1)

Example: If 10% of control patients and 5% of treated patients experience an event, the risk reduction is 0.10 - 0.05 = 0.05 (or 5 percentage points).

3. Interpretation of Risk Reduction

Details: A positive RR indicates the treatment reduces risk. The larger the RR, the greater the treatment effect. RR is often expressed as a percentage (multiply by 100).

4. Using the Calculator

Tips: Enter event rates as decimals between 0 and 1 (e.g., 10% = 0.10). The control rate should typically be higher than the treatment rate for meaningful interpretation.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between RR and RRR?
A: RR is absolute risk reduction (difference in rates), while RRR (relative risk reduction) is the reduction relative to control rate: \( (E_c-E_t)/E_c \).

Q2: When is risk reduction most useful?
A: RR is particularly helpful when event rates are high, as it shows the actual clinical impact more clearly than relative measures.

Q3: What's a good risk reduction value?
A: This depends on context. Even small RRs can be important for common or serious outcomes, while larger RRs are needed for rare or minor outcomes.

Q4: How does RR relate to NNT?
A: Number Needed to Treat (NNT) is the reciprocal of RR: \( NNT = 1/RR \). It tells how many patients need treatment to prevent one event.

Q5: Can RR be negative?
A: Yes, a negative RR means the treatment increased risk compared to control, which could indicate harm or ineffective treatment.