TimelyScholarFree Tools › Confidence Interval Calculator
Calculate a 90%, 95% or 99% confidence interval for a mean from its SD and sample size, or for a proportion using the Wilson score method.
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| 95% CI for the mean | 69.456 to 75.344 |
|---|---|
| Margin of error | ± 2.944 |
| Standard error | 1.4609 |
| Critical t | 2.0154 (df = 44) |
And the confidence level.
Mean, SD and n, or successes and n.
A confidence interval gives a range of plausible values for a population parameter. A 95% interval is built so that, over many repeated samples, 95% of such intervals would contain the true value.
For a mean, the interval uses the t distribution. For a proportion, the Wilson score interval performs well even with small samples or proportions near 0 or 100%.
With small samples the t distribution is wider than the normal, so using t keeps the interval honest.