Math & Statistics

What Is a Confidence Interval?

A confidence interval is a range of values, calculated from sample data, that is likely to contain the true value of a population measure such as a mean. A 95% confidence interval means that if the sampling process were repeated many times, about 95% of the intervals calculated would contain the true value.

Approximate Formula

For a mean: sample mean ± about 1.96 × standard error (for 95% confidence with larger samples).

Width

Larger samples and less variable data produce narrower, more precise intervals.

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🔗 Related Terms

Standard Error Margin of Error Normal Distribution Sample vs. Population

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Last updated: September 29, 2026. This definition is for general educational purposes only. It is not financial, investment, tax, legal, or medical advice, and it does not recommend any product or course of action. For decisions about your own situation, consult a qualified professional.