Confidence Interval Interpretation
A 95% confidence interval means that if sampling and interval calculation are repeated many times, about 95% of the calculated intervals will contain the true parameter. The interval is constructed from sample data using the formula: estimate ± (critical value × standard error).
Real World
NHS England publishes 95% confidence intervals alongside waiting-time statistics; the interval tells policymakers how precise the estimate is, not that any single interval definitely contains the true average.
Exam Focus
Never write 'there is a 95% probability the parameter lies in this interval' — describe the long-run procedure instead.
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