Absolute Risk Reduction Confidence Interval Calculator

Confidence Interval Formula:

\[ CI = ARR \pm 1.96 \times SE \]

95% Confidence Interval:

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Absolute Risk Reduction Confidence Interval?

The Absolute Risk Reduction (ARR) Confidence Interval provides a range of plausible values for the true treatment effect in a clinical study. It quantifies the uncertainty around the point estimate of ARR and helps determine if the observed effect is statistically significant.

2. How Does the Calculator Work?

The calculator uses the standard confidence interval formula:

\[ CI = ARR \pm 1.96 \times SE \]

Where:

\( ARR \) — Absolute Risk Reduction (proportion)
\( SE \) — Standard Error of ARR
\( 1.96 \) — Z-score for 95% confidence level

Explanation: The formula calculates the margin of error around the ARR point estimate, providing a range where the true population parameter likely falls with 95% confidence.

3. Importance of Confidence Interval Calculation

Details: Confidence intervals are crucial for interpreting clinical trial results as they provide information about the precision of the estimate and help assess clinical significance beyond statistical significance.

4. Using the Calculator

Tips: Enter the Absolute Risk Reduction as a proportion (e.g., 0.15 for 15%) and the Standard Error. Both values must be positive, with ARR typically between 0 and 1.

5. Frequently Asked Questions (FAQ)

Q1: What does a 95% confidence interval mean?
A: It means that if the same study were repeated many times, 95% of the calculated confidence intervals would contain the true population parameter.

Q2: How is standard error calculated for ARR?
A: Standard error for ARR is typically calculated using the formula: \( SE = \sqrt{\frac{p_1(1-p_1)}{n_1} + \frac{p_2(1-p_2)}{n_2}} \), where p₁ and p₂ are event rates in treatment and control groups.

Q3: When is ARR considered statistically significant?
A: When the 95% confidence interval does not include zero, indicating the treatment effect is unlikely due to chance alone.

Q4: What's the difference between ARR and RRR?
A: ARR is the absolute difference in event rates, while RRR (Relative Risk Reduction) is the proportional reduction in events compared to control.

Q5: Can I use this for other confidence levels?
A: This calculator uses 1.96 for 95% CI. For 90% CI use 1.645, for 99% CI use 2.576 as the z-score multiplier.