It is customary to approximate the standard error of the sample mean $\sigma / \sqrt { n }$
by substituting the sample standard deviation s for $\sigma$
in the formula: SE( $\bar { X }$
)= $\sigma / \sqrt { n }$
.

Question

It is customary to approximate the standard error of the sample mean $\sigma / \sqrt { n }$ 
by substituting the sample standard deviation s for $\sigma$ 
in the formula: SE( $\bar { X }$ 
)= $\sigma / \sqrt { n }$ 
.

Quizplus · Accepted Answer

The standard error of the sample mean is often approximated by using the sample standard deviation (s) instead of the population standard deviation ($\sigma$) when $\sigma$ is unknown.

It Is Customary to Approximate the Standard Error of the Sample