Suppose that we have assumed the straight-line regression model Y = β0 + β 1 x 1 + ? but the response is affected by a second variable x 2 such that the true regression function is E ( Y )= β 0 + β 1...

Suppose that we have assumed the straight-line regression model

Y
= β0 + β₁
x
₁+ ?

but the response is affected by a second variable
x
₂such that the true regression function is

E(Y
)= β₀+ β₁
x
₁+ β₂
x
₂

Is the estimator of the slope in the simple linear regression model unbiased?