Consider the regression equation
![2200_Regression equation.png](https://secure.tutorsglobe.com/CMSImages/2200_Regression%20equation.png)
where x2, is exogenous and x3, is endogenous.
Which of the following conditions must a variable satisfy to be useful as an instrument for x3,?
You may select more than one condition. You will receive credit for each correct condition. You will lose marks for selecting an incorrect condition. The lowest mark that you can score for this question is zero.
![56_Regression equation.png](https://secure.tutorsglobe.com/CMSImages/56_Regression%20equation.png)