Confidence Interval Calculator
Calculate confidence intervals for common estimates used in clinical and academic research.
Required Terms Explained
Mean is the average value in your sample. Standard deviation describes how spread out the observations are. Sample size is the number of observations. For a proportion, events is the number of patients with the outcome and total sample size is the denominator. The confidence interval becomes narrower when sample size increases or variability decreases.
About this method
A confidence interval gives a plausible range for the true population value. Narrow intervals indicate more precise estimates; wide intervals indicate greater uncertainty.
Frequently Asked Questions
What does a 95% CI mean?
It means that repeated studies using the same method would produce intervals containing the true value about 95% of the time.
Is confidence interval better than p-value?
They answer different questions. CIs show precision and plausible effect size, while p-values test compatibility with the null hypothesis.
Why is my CI wide?
Wide CIs usually result from small samples, high variability, or rare outcomes.