In Practice, the Standard Error of the Difference Between Means $\sqrt { \left. \frac { \left( \sigma _ { 1 } \right) ^ { 2 } } { n _ { 1 } } + \frac { ( \sigma } { n _ { 2 } } \right) ^ { 2 } }$

Multiple Choice

In practice, the standard error of the difference between means is estimated by.

A) $\sqrt { \left. \frac { \left( \sigma _ { 1 } \right) ^ { 2 } } { n _ { 1 } } + \frac { ( \sigma } { n _ { 2 } } \right) ^ { 2 } }$
B) $s _ { \bar { x } _ { 1 } - \bar { x } _ { 2 } }$
C) $\left( s _ { \bar { x } _ { 1 } - \bar { x } _ { 2 } } \right) ^ { 2 }$
D) $\frac { \sigma _ { 1 } } { n _ { 1 } } + \frac { \sigma _ { 2 } } { n _ { 2 } }$