Confidence interval


A range of likely values for an unknown parameter.

In general: Point Estimate ± (Reliability factor x std err)

Using z-statistic: ± z𝛂/2 𝝈

Using t-statistic: X̄ ± t𝛂/2 s

For a normal distribution, the confidence intervals are:

90%: ±1.65 standard deviations

95%: ±1.96 standard deviations

99%: ±2.58 standard deviations

See also: Test statistic