When determining the sample size needed to achieve a particular error estimate you need to know $\sigma$ What are two methods of estimating $\sigma$ if $\sigma$ is unknown?

Question

When determining the sample size needed to achieve a particular error estimate you need to know $\sigma$ What are two methods of estimating  $\sigma$ if  $\sigma$  is unknown?

Quizplus · Accepted Answer

The Answer of When determining the sample size needed to achieve a particular error estimate you need to know $\sigma$ What are two methods of estimating  $\sigma$ if  $\sigma$  is unknown?

When Determining the Sample Size Needed to Achieve a Particular σ\sigmaσ

When Determining the Sample Size Needed to Achieve a Particular $\sigma$