What is a confidence interval?

A range that is likely to contain the true population mean. E.g. 95% CI means we are 95% confident the true mean lies in that interval.

Which confidence levels?

Common levels: 90%, 95%, 99%. We use the corresponding z-values (e.g. 1.645, 1.96, 2.576).

CI for mean: mean, standard deviation, sample size n, confidence % (90/95/99). CI = mean ± z × (s/√n).

Mean (sample mean)

Standard deviation (s)

Sample size (n)

Confidence (%)

What is a confidence interval?: A range that is likely to contain the true population mean. E.g. 95% CI means we are 95% confident the true mean lies in that interval.
Which confidence levels?: Common levels: 90%, 95%, 99%. We use the corresponding z-values (e.g. 1.645, 1.96, 2.576).

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