A range of values that likely contains the true population parameter, with a specified level of confidence (usually 95%). It provides information about the precision and uncertainty of an estimate.
Introduced by Jerzy Neyman in 1937 as an improvement over point estimates. 'Confidence' refers to the long-run probability that such intervals contain the true parameter, though the term often causes confusion about what the interval actually represents.
A 95% confidence interval doesn't mean there's a 95% chance the true value is in that range—it means if you repeated the study 100 times, about 95 of those intervals would contain the true value! It's about the procedure, not the specific interval.
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