Final answer:
When developing an interval estimate and the population standard deviation is unknown, the sample standard deviation must be used as an estimate. This allows statisticians to calculate a confidence interval with close-enough results.
Step-by-step explanation:
When developing an interval estimate and the population standard deviation is unknown, we assume that the sample standard deviation must be used. In practice, statisticians use the sample standard deviation as an estimate for the population standard deviation. This allows them to calculate a confidence interval with close-enough results. The confidence interval is a range of values likely to include the unknown population parameter.