a. Assume the following regression model where i Y₁ =B₁X₁1 + B₂X₁2 + €į, i = 1, ..., n iid N (0,0²), o > 0 holds true. Suppose that ΣX1X2 = 0. Show that the least squares estimators ₁ and ₂ from the multiple regression are the same as if we were to fit separate, simple regressions on X₁ and X₂.

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a. Assume the following regression model
where Ei
Y₁ = B₁1X₁1 + B₂X₁2 + €į, i=1,...,n
iid
N(0, o²), σ > 0 holds true. Suppose that
ΣX1X2 = 0.
2
Show that the least squares estimators ₁ and ₂ from the multiple regression are the
same as if we were to fit separate, simple regressions on X₁ and X₂.
Transcribed Image Text:a. Assume the following regression model where Ei Y₁ = B₁1X₁1 + B₂X₁2 + €į, i=1,...,n iid N(0, o²), σ > 0 holds true. Suppose that ΣX1X2 = 0. 2 Show that the least squares estimators ₁ and ₂ from the multiple regression are the same as if we were to fit separate, simple regressions on X₁ and X₂.
b. Consider the following functions of the random variables X₁, X2, X3, and X4:
· [X1 + X2 + X3 + X4]
Y₁
=
1
Y2 = [X₁ + X2] - [X3 + X4]
2
(i) State the above in the matrix notation.
(ii) Find the expectation of the random vector Y
(iii) Find the variance-covariance matrix of Y =
= Y₂
H
Transcribed Image Text:b. Consider the following functions of the random variables X₁, X2, X3, and X4: · [X1 + X2 + X3 + X4] Y₁ = 1 Y2 = [X₁ + X2] - [X3 + X4] 2 (i) State the above in the matrix notation. (ii) Find the expectation of the random vector Y (iii) Find the variance-covariance matrix of Y = = Y₂ H
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