A confidence interval (CI) gives a range of plausible values for a population parameter based on a sample. A 95% CI means: if we repeated this study many times, 95% of the resulting intervals would contain the true population value.
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Pro Tip
Increasing sample size narrows the CI (more precision). Doubling n reduces the margin of error by a factor of √2 ≈ 1.41.
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Did You Know?
A 95% confidence interval does NOT mean there is a 95% probability the true value is in that interval — it either is or it isn't. The 95% refers to the long-run frequency of the method.
References
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