$$\bar { x } _ { 1 } - \bar { x } _ { 2 } \text { is an unbiased statistic used to estimate } \mu _ { 1 } - \mu _ { 2 } \text {. }$$

True/False

$$\bar { x } _ { 1 } - \bar { x } _ { 2 } \text { is an unbiased statistic used to estimate } \mu _ { 1 } - \mu _ { 2 } \text {. }$$ $$\text { For two independent samples, } \sigma _ { \bar { x } _ { 1 } - \bar { x } _ { 2 } } = \sqrt { \frac { \sigma _ { 1 } ^ { 2 } } { n _ { 1 } } - \frac { \sigma _ { 2 } ^ { 2 } } { n _ { 2 } } } \text {. }$$