In the calculation of confidence interval, how can we know the exact value of population standard deviation? For the case of investigating the height of a population, it should be even harder to obtain than the actual population mean?
Hi @ksefong
In practice, the population standard deviation is unknown. Instead, we use the sample standard deviation as an estimate of \sigma.
When calculating confidence intervals, if \sigma is unknown and the sample size is large (n > 30), the sample standard deviation is often substituted, and the normal distribution is used.
For smaller sample sizes, the t-distribution is used.
Hope it helps! Feel free to ask if you need further assistance.