Problem 3. Consider a very large random sample of (Yi, Xi, Zi, Qi), where Yi = Bo+ BıXi+Ui, = 0.9, ởzx = 0.7, and Z₁ and Q₁ are some variables. Suppose o 4,0² = 3, 02 = 2, σχυ ozu = Y, for some number 7, and Q₁ is independent of (Yi, Xi, Zi) (perhaps it was generated randomly on a computer without any connection to the data we have). Let us define a new variable Ri= Zi + Qi. (a) Suppose we run OLS regression of Y; on X, and a constant. Will this result in a consistent estimator of B₁? (b) Suppose y = 0. Is Z; a valid instrumental variable? (c) Suppose y = 0. Is Rį a valid instrumental variable? (d) Suppose y 0. Let 3z denote the TSLS estimator of 3₁ that uses Z; as the instrumental variable. Let bz denote the probability limit of 3z, i.e., BÔz →p bz as n → ∞. Using the information provided above, find bz. Hint: bz could depend on y.

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Problem 3. Consider a very large random sample of (Yi, Xi, Zi, Qi), where
Yi = Bo+ BıX+U,
=
and Z₁ and Q₁ are some variables. Suppose o = 4, 0²/2 3, o2 = 2, oxu = 0.9, σzx = 0.7,
ozu = Y, for some number y, and Q₁ is independent of (Yi, Xi, Zi) (perhaps it was generated
randomly on a computer without any connection to the data we have). Let us define a new variable
Ri= Zi + Qi.
(a) Suppose we run OLS regression of Y; on X; and a constant. Will this result in a consistent
estimator of B₁?
(b) Suppose y = 0. Is Z, a valid instrumental variable?
(c) Suppose y
= 0. Is R₂ a valid instrumental variable?
(d) Suppose y # 0. Let 3z denote the TSLS estimator of 3₁ that uses Z; as the instrumental
variable. Let bz denote the probability limit of z, i.e., z →p bz as n → ∞. Using the
information provided above, find bz. Hint: bz could depend on y.
Transcribed Image Text:Problem 3. Consider a very large random sample of (Yi, Xi, Zi, Qi), where Yi = Bo+ BıX+U, = and Z₁ and Q₁ are some variables. Suppose o = 4, 0²/2 3, o2 = 2, oxu = 0.9, σzx = 0.7, ozu = Y, for some number y, and Q₁ is independent of (Yi, Xi, Zi) (perhaps it was generated randomly on a computer without any connection to the data we have). Let us define a new variable Ri= Zi + Qi. (a) Suppose we run OLS regression of Y; on X; and a constant. Will this result in a consistent estimator of B₁? (b) Suppose y = 0. Is Z, a valid instrumental variable? (c) Suppose y = 0. Is R₂ a valid instrumental variable? (d) Suppose y # 0. Let 3z denote the TSLS estimator of 3₁ that uses Z; as the instrumental variable. Let bz denote the probability limit of z, i.e., z →p bz as n → ∞. Using the information provided above, find bz. Hint: bz could depend on y.
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