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About the Confidence Interval Calculator
This calculator computes confidence intervals for population means, proportions, and the difference between two groups. Enter your sample data and you get the lower and upper bounds of the interval, along with the margin of error and the critical value.
For means it applies the standard formula x̄ ± t × (s / √n), where t comes from the t-distribution with n-1 degrees of freedom. Proportions use the z-based interval p̂ ± z × √(p̂(1-p̂)/n). You provide the sample mean or proportion, sample size, standard deviation, and a confidence level such as 90%, 95%, or 99%. A larger sample yields a narrower interval, so add observations if the range feels too wide.
- Choose what you want to estimate: a mean, a proportion, or a difference between groups.
- Enter the sample size, mean or proportion, and standard deviation where required.
- Pick a confidence level and read the lower and upper bounds from the results.