TEST BANK FOR
Introduction to Econometrics 3rd Edition by H STOCK JAMES & W. WATSON
MARK
FULL TEST BANK!!!
,Chapter 2
Review of Probability
2.1. (a) Probability distribution function for Y
Outcome (number of heads) Y=0 Y=1 Y=2
Probability 0.25 0.50 0.25
(b) Cumulative probability distribution function for Y
Outcome (number of heads) Y0 0Y1 1Y2 Y2
Probability 0 0.25 0.75 1.0
(c) Y = E(Y ) = (0 0.25) + (1 0.50) + (2 0.25) = 1.00 . F →
d
Fq, .
Using Key Concept 2.3: var(Y ) = E(Y 2 ) −[E(Y )]2 ,
and
(ui |Xi )
so that
var(Y ) = E(Y 2 ) −[E(Y )]2 = 1.50 − (1.00)2 = 0.50.
2.2. We know from Table 2.2 that Pr (Y = 0) = 022, Pr (Y = 1) = 078, Pr ( X = 0) = 030,
Pr( X = 1) = 070. So
(a) Y = E(Y ) = 0 Pr (Y = 0) + 1 Pr (Y = 1)
= 0 022 + 1 078 = 078,
X = E( X ) = 0 Pr ( X = 0) + 1 Pr ( X = 1)
= 0 030 + 1 070 = 070
(b) 2 = E[( X − )2 ]
X X
= (0 − 0.70) Pr ( X = 0) + (1 − 0.70)2 Pr ( X = 1)
2
= (−070)2 030 + 0302 070 = 021,
Y2 = E[(Y − Y )2 ]
= (0 − 0.78)2 Pr (Y = 0) + (1 − 0.78)2 Pr (Y = 1)
= (−078)2 022 + 0222 078 = 01716
YTREW
, YTREW
(c) XY = cov (X , Y ) = E[( X − X )(Y − Y )]
= (0 − 0.70)(0 − 0.78) Pr( X = 0, Y = 0)
+ (0 − 070)(1 − 078) Pr ( X = 0 Y = 1)
+ (1 − 070)(0 − 078) Pr ( X = 1 Y = 0)
+ (1 − 070)(1 − 078) Pr ( X = 1 Y = 1)
= (−070) (−078) 015 + (−070) 022 015
+ 030 (−078) 007 + 030 022 063
= 0084,
XY 0084
corr (X , Y ) = = = 04425
XY 021 01716
2.3. For the two new random variables W = 3 + 6 X and V = 20 − 7Y , we have:
(a) E(V ) = E(20 − 7Y ) = 20 − 7E(Y ) = 20 − 7 078 = 1454,
E(W ) = E(3 + 6X ) = 3 + 6E( X ) = 3 + 6 070 = 72
(b) 2 = var(3 + 6X ) = 62 2 = 36 021 = 756,
W X
V = var(20 − 7Y ) = (−7) Y2 = 49 01716 = 84084
2 2
(c) WV = cov(3 + 6X , 20 − 7Y ) = 6 (−7) cov(X , Y ) = −42 0084 = −3528
WV −3528
corr (W , V ) = = = −04425
WV 756 84084
2.4. (a) E( X 3 ) = 03 (1− p) +13 p = p
(b) E( X k ) = 0k (1− p) +1k p = p
(c) E( X ) = 0.3 , and var(X) = E(X2)−[E(X)]2 = 0.3 −0.09 = 0.21. Thus = 0.21 = 0.46.
var( X ) = E( X 2 ) −[E( X )]2 = 0.3 − 0.09 = 0.21 = 0.21 = 0.46. To compute the skewness, use
the formula from exercise 2.21:
E( X − )3 = E( X 3 ) − 3[E( X 2 )][E( X )] + 2[E( X )]3
= 0.3 − 3 0.32 + 2 0.33 = 0.084
Alternatively, E( X − )3 =[(1− 0.3)3 0.3] +[(0 − 0.3)3 0.7] = 0.084
Thus, skewness = E( X − )3/ 3 = 0.084/0.463 = 0.87.
To compute the kurtosis, use the formula from exercise 2.21:
E( X − )4 = E( X 4 ) − 4[E( X )][E( X 3 )] + 6[E( X )]2 [E( X 2 )] − 3[E( X )]4
= 0.3 − 4 0.32 + 6 0.33 − 3 0.34 = 0.0777
Alternatively, E( X − )4 =[(1− 0.3)4 0.3] +[(0 − 0.3)4 0.7] = 0.0777
Thus, kurtosis is E( X − )4/ 4 = 0.0777/0.464 =1.76
, 4 Stock/Watson • Introduction to Econometrics, Third Edition
2.5. Let X denote temperature in F and Y denote temperature in C. Recall that Y = 0 when X = 32 and
Y =100 when X = 212; this implies Y = (100/180) ( X − 32) or Y = −17.78 + (5/9) X. Using Key
Concept 2.3, X = 70oF implies that Y = −17.78 + (5/9) 70 = 21.11C, and X = 7oF implies
Y = (5/9) 7 = 3.89C.
2.6. The table shows that Pr ( X = 0, Y = 0) = 0037, Pr ( X = 0, Y = 1) = 0622,
Pr ( X = 1, Y = 0) = 0009, Pr ( X = 1, Y = 1) = 0332, Pr ( X = 0) = 0659, Pr ( X = 1) = 0341,
Pr(Y = 0) = 0046, Pr (Y = 1) = 0954.
(a) E(Y ) = Y = 0 Pr(Y = 0) + 1 Pr (Y = 1)
= 0 0046 +1 0954 = 0954
#(unemployed)
(b) Unemployment Rate =
#(labor force)
= Pr (Y = 0) = 1 − Pr(Y = 1) = 1 − E(Y ) = 1 − 0954 = 0.046
(c) Calculate the conditional probabilities first:
Pr ( X = 0, Y = 0) 0037
Pr (Y = 0| X = 0) = = = 0056,
Pr ( X = 0) 0659
Pr ( X = 0, Y = 1) 0622
Pr (Y = 1| X = 0) = = = 0944,
Pr ( X = 0) 0659
Pr ( X = 1, Y = 0) 0009
Pr (Y = 0| X = 1) = = = 0026,
Pr ( X = 1) 0341
Pr ( X = 1, Y = 1) 0332
Pr (Y = 1| X = 1) = = = 0974
Pr ( X = 1) 0341
The conditional expectations are
E(Y|X = 1) = 0 Pr (Y = 0| X = 1) +1 Pr (Y = 1| X = 1)
= 0 0026 + 1 0974 = 0974,
E(Y|X = 0) = 0 Pr (Y = 0| X = 0) + 1 Pr (Y = 1|X = 0)
= 0 0056 +1 0944 = 0944
(d) Use the solution to part (b),
Unemployment rate for college graduates = 1 − E(Y|X = 1) = 1 − 0.974 = 0.026
Unemployment rate for non-college graduates = 1 − E(Y|X = 0) = 1 − 0.944 = 0.056
(e) The probability that a randomly selected worker who is reported being unemployed is a
college graduate is
Pr ( X = 1, Y = 0) 0009
Pr ( X = 1|Y = 0) = = = 0196
Pr (Y = 0) 0046
The probability that this worker is a non-college graduate is
Pr ( X = 0|Y = 0) = 1 − Pr ( X = 1|Y = 0) = 1 − 0196 = 0804
©2011 Pearson Education, Inc. Publishing as Addison Wesley