Answers to Selected 
Exercises 
For  
Principles of Econometrics, Fourth Edition 
R. CARTER HILL 
Louisiana State University 
WILLIAM E. GRIFFITHS 
University of Melbourne 
GUAY C. LIM 
University of Melbourne 
 
 
 
JOHN WILEY & SONS, INC 
New York / Chichester / Weinheim / Brisbane / Singapore / Toronto 
 
CONTENTS 
 
 
 
Answers for Selected Exercises in: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  Probability Primer 
  Chapter 2 
  Chapter 3 
  Chapter 4 
  Chapter 5 
  Chapter 6 
  Chapter 7 
  Chapter 8 
  Chapter 9 
  Chapter 10 
  Chapter 11 
  Chapter 15 
  Chapter 16 
  Appendix A  Mathematical Tools 
  Appendix B 
  Appendix C 
 
 
 
 
The Simple Linear Regression Model 
 
 
Interval Estimation and Hypothesis Testing   
 
Prediction, Goodness of Fit and Modeling Issues 
 
The Multiple Regression Model 
Further Inference in the Multiple Regression Model    
Using Indicator Variables 
 
 
Heteroskedasticity 
Regression with Time Series Data: Stationary Variables 
Random Regressors and Moment Based Estimation  
 
Simultaneous Equations Models 
Panel Data Models 
 
Qualitative and Limited Dependent Variable Models 
 
 
 
 
 
Probability Concepts   
 
Review of Statistical Inference 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
     1 
     3 
    12 
    16 
    22 
    29 
    36 
    44 
    51 
    58 
    60 
    64 
    66 
    69 
    72 
    76 
 
 
29 August, 2011 
PROBABILITY PRIMER 
Exercise Answers 
EXERCISE P.1 
(a) 
X is a random variable because attendance is not known prior to the outdoor concert.  
(b) 
(c) 
(d) 
1100 
3500  
6,000,000  
EXERCISE P.3 
 
0.0478  
EXERCISE P.5 
(a) 
0.5.  
(b) 
0.25 
EXERCISE P.7 
(a) 
 
f c  
( )
0.15 
0.40 
0.45 
 
(b) 
(c) 
(d) 
1.3 
0.51 
f
(0,0) 0.05
f
C
(0)
f
B
(0) 0.15 0.15 0.0225
 
1 
Probability Primer, Exercise Answers, Principles of Econometrics, 4e 
 
2 
(e) 
 
A 
5000 
6000 
7000 
f a  
( )
0.15 
0.50 
0.35 
 
(f) 
1.0 
EXERCISE P.11 
(a) 
(b) 
(c) 
(d) 
(e) 
 0.0289 
 0.3176 
0.8658 
 0.444 
1.319 
EXERCISE P.13 
(a) 
(b) 
(c) 
 0.1056 
 0.0062 
 (a) 0.1587 (b) 0.1265 
EXERCISE P.15 
(a) 
(b) 
(c) 
(d) 
(e) 
(f) 
9 
1.5 
0 
109 
−66 
−0.6055 
EXERCISE P.17 
x
(a) 
2
(b) 
(c) 
(d) 
(e) 
(f) 
a b x
4
(
1
14 
34 
f
  (4)
f
(0,
36 
(5)
f
(1,
y
)
f
x
3
x
4
)
 
f
y
)
(6)
f
 
(2,
y
)
 
CHAPTER  2 
Exercise Answers 
EXERCISE 2.3 
(a) 
The  line  drawn  for  part  (a)  will  depend  on  each  student’s  subjective  choice  about  the 
position of the line.  For this reason, it has been omitted. 
 
1.514286
b  
2
b 
1 10.8
(b) 
 
Figure xr2.3 Observations and fitted line
 
 
0
1
8
6
4
2
1
2
3
x
4
y
Fitted values
5
6
 
 
 
y 
 
x 
 ˆ
y 
5.5
3.5
5.5
 
 
 
(c) 
 
 
 
3 
Chapter 2, Exercise Answers Principles of Econometrics, 4e    
4 
Exercise 2.3 (Continued) 
(d) 
 
ˆie  
0.714286 
0.228571 
−1.257143 
0.257143 
−1.228571 
1.285714 
 
 
 
(e)  
 
ie 
ˆ
0.
 
ix e 
 
ˆ
i
0
 
240
b  
1
  is  an  estimate  of  the  number  of  sodas  sold  when  the 
The  intercept  estimate 
temperature is 0 degrees Fahrenheit.  Clearly, it is impossible to sell 240 sodas and so 
this estimate should not be accepted as a sensible one. 
 
b   is an estimate of the increase in sodas sold when temperature 
The slope estimate 
2
increases by 1 Fahrenheit degree.  One would expect the number of sodas sold to increase 
as temperature increases. 
 ˆ
y  
240 8 80
 
400
 
She predicts no sodas will be sold below 30F. 
A graph of the estimated regression line: 
Figure xr2.6 Regression line
0
0
6
0
0
4
0
0
2
y
0
0
0
2
-
0
20
40
x
60
80
100
 
EXERCISE 2.6 
(a) 
8
 
 
 
(b) 
 
(c) 
 
(d) 
Chapter 2, Exercise Answers Principles of Econometrics, 4e    
5 
EXERCISE 2.9 
(a) 
 
 
 
Figure xr2.9a Occupancy Rates
100
90
80
70
60
50
40
30
0
2
4
6
8
10
12
14
16
18
20
22
24
26
month, 1=march 2003,.., 25=march 2005
percentage motel occupancy
percentage competitors occupancy
 
The repair period comprises those months between the two vertical lines. The graphical 
evidence suggests that the damaged motel had the higher occupancy rate before and after 
the  repair  period.  During the  repair  period,  the  damaged  motel  and  the  competitors  had 
similar occupancy rates. 
A plot of MOTEL_PCT against COMP_PCT yields: 
Figure xr2.9b Observations on occupancy
 
 
 
(b) 
100
90
80
70
60
50
40
y
c
n
a
p
u
c
c
o
 
l
e
t
o
m
 
e
g
a
t
n
e
c
r
e
p
 
40
50
60
70
80
percentage competitors occupancy
 
 
There appears to be a positive relationship the two variables. Such a relationship may exist 
as both the damaged motel and the competitor(s) face the same demand for motel rooms.  
Chapter 2, Exercise Answers Principles of Econometrics, 4e    
6 
Exercise 2.9 (continued) 
21.40 0.8646
(c)  _
MOTEL PCT
The  competitors’  occupancy  rates  are  positively  related  to  motel  occupancy  rates,  as 
expected. The regression indicates that for a one percentage point increase in competitor 
occupancy  rate,  the  damaged  motel’s  occupancy  rate  is  expected  to  increase  by  0.8646 
percentage points. 
COMP PCT
_
. 
(d) 
 
l
s
a
u
d
s
e
r
i
30
20
10
0
-10
-20
-30
Repair period
0
4
8
12
16
20
24
28
month, 1=march 2003,.., 25=march 2005
Figure xr2.9(d) Plot of residuals against time 
 
The residuals during the occupancy period are those between the two vertical lines. All 
except  one  are  negative,  indicating  that  the  model  has  over-predicted  the  motel’s 
occupancy rate during the repair period.  
(e)  We  would  expect  the  slope  coefficient  of  a  linear  regression  of  MOTEL_PCT  on 
RELPRICE to be negative, as the higher the relative price of the damaged motel’s rooms, 
the lower the demand will be for those rooms, holding other factors constant. 
  _
MOTEL PCT
166.66 122.12
RELPRICE
 
 
(f) 
 
 
The estimated regression is: 
  _
MOTEL PCT
 In the non-repair period, the damaged motel had an estimated occupancy rate of 79.35%. 
During the repair period, the estimated occupancy rate was 79.35−13.24 = 66.11%. Thus, 
it appears the motel did suffer a loss of occupancy and profits during the repair period. 
79.3500 13.2357
REPAIR
 
(g) 
 From the earlier regression, we have 
 
 
 
  
MOTEL
0
MOTEL
1
 
b 
1 79.35%
b
1
b
2
 
79.35 13.24 66.11%