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Mathematics

Confidence Intervals for Population Means and Proportions

Quick fact

A 95% confidence interval does NOT mean there's a 95% chance the true parameter lies in that particular interval. Instead, it means that if you repeated the sampling process many times, 95% of the intervals you'd construct would contain the true parameter.

Why this is interesting

Imagine you poll 1,000 voters and find 52% support a candidate. How confident can you be that the true support in the whole population is close to 52%? A confidence interval gives you a range, say 49% to 55%, with a measured level of certainty.