Since the Mean Of $\hat { \beta } _ { 1 } \text { is } E ( \hat { \beta }_{1} ) = \beta _ { 1 } \text {, then } \hat { \beta }_{1}$

Short Answer

Since the mean of $\hat { \beta } _ { 1 } \text { is } E ( \hat { \beta }_{1} ) = \beta _ { 1 } \text {, then } \hat { \beta }_{1}$ is an __________ estimator of $\beta _ { 1 }$ .