The bias of an estimator  is defined as
| 
 
(1)
 
 | 
It is therefore true that
| 
 
(2)
 
 | |||
| 
 
(3)
 
 | 
An estimator for which  is said to be unbiased
 estimator.
The bias of an estimator  is defined as
| 
 
(1)
 
 | 
It is therefore true that
| 
 
(2)
 
 | |||
| 
 
(3)
 
 | 
An estimator for which  is said to be unbiased
 estimator.
Weisstein, Eric W. "Estimator Bias." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/EstimatorBias.html