If the Causal Effect Is Different for Different People, Then $Y _ { i } = \beta _ { 0 } + \beta _ { 1 } X _ { i } + u _ { i }$

Short Answer

If the causal effect is different for different people, then the population regression equation for a binary treatment variable Xi, can be written as a. $Y _ { i } = \beta _ { 0 } + \beta _ { 1 } X _ { i } + u _ { i }$ .
b. $Y _ { i } = \beta _ { 0 } + \beta _ { 1 i } X _ { i } + u _ { i }$ .
c. $Y _ { i } = \beta _ { 0 i } + \beta _ { 1 i } X _ { i } + u _ { i }$ .
d. $Y _ { i } = \beta _ { 0 } + \beta _ { 1 } G _ { i } + \beta _ { 2 } D _ { t } + u _ { i }$ .