Calculate Confidence Interval by Hand
Introduction & Importance
Calculating confidence intervals by hand is a crucial statistical skill…
How to Use This Calculator
- Enter your sample size, mean, and standard deviation.
- Select your desired confidence level.
- Click ‘Calculate’.
Formula & Methodology
The formula for calculating a confidence interval is…
Real-World Examples
Example 1: A survey of 100 people found a mean satisfaction score of 8.5 with a standard deviation of 1.2. What’s the 95% confidence interval?
Example 2: A study of 500 patients found a mean recovery time of 12.3 days with a standard deviation of 2.1. What’s the 99% confidence interval?
Example 3: A poll of 200 voters found a mean support of 55% with a standard deviation of 3.5. What’s the 90% confidence interval?
Data & Statistics
| Confidence Level | Z-Score | Margin of Error |
|---|---|---|
| 90% | 1.645 | 1.645 * (SD / √n) |
| 95% | 1.96 | 1.96 * (SD / √n) |
| 99% | 2.576 | 2.576 * (SD / √n) |
Expert Tips
- Always use the correct Z-score for your desired confidence level.
- Ensure your sample size is large enough for accurate results.
- Consider using a t-distribution for smaller sample sizes.
Interactive FAQ
What is a confidence interval?
A confidence interval is a range of values around a sample statistic…
Why is it important?
Confidence intervals help us understand the reliability of our sample…
Learn more about confidence intervals from Stats.govt.nz
Understand confidence intervals better with Penn State’s guide