In the model y = + 1 x 1 + 2 x 2

In the model μ_y = α + β₁ x₁ + β₂ x₂, suppose that x₂ is an indicator variable for gender, equaling 1 for females and 0 for males.
a. We set x₂ = 0 if we want a predicted mean without knowing gender.
b. The slope effect of x₁ is β₁ for males and β₂ for females.
c. β₂ is the difference between the population mean of y for females and for males.
d. β₂ is the difference between the population mean of y for females and males, for all those subjects having x₁ fixed, such as x₁ = 10.