What does a 95% confidence interval mean?
mediumAnswer
- If we repeated the sampling and interval construction procedure many times, about 95% of the resulting intervals would contain the true parameter.
- It's NOT 'there is a 95% probability the parameter is in this specific interval' — the parameter is fixed and the interval is random.
- Interpret CIs as long-run coverage guarantees.
Check yourself — multiple choice
- The parameter is in this interval with probability 0.95
- The interval covers the parameter 95% of the time under repeated sampling
- The CI depends only on the point estimate
- Wider CIs mean higher confidence in a point estimate
Frequentist CI = long-run coverage rate, not a Bayesian statement.
#confidence-interval#estimation
Practise Statistics Fundamentals
215 interview questions in this topic.