Theoretical Economics Letters, 2013, 3, 202-210
http://dx.doi.org/10.4236/tel.2013.34034 Published Online August 2013 (http://www.scirp.org/journal/tel)
Capacity Choice in a Private Duopoly: A Unilateral
Externality Case*
Yasuhiko Nakamura
College of Economics, Nihon University, Tokyo, Japan
Email: yasuhiko. r.nakamura@gmail.com
Received May 29, 2013; revised June 29, 2013; accepted July 18, 2013
Copyright © 2013 Yasuhiko Nakamura. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
This paper studies capacity choice in a quantity-setting and price-setting private duopoly with differentiated goods
wherein either of two firms has a price-raising effect on the price level of the product of the opponent firm. In both
quantity-setting and price-setting competition, whether the price-raising effect of the product of one firm on the price
level of the other firm’s product is strong or weak strictly depends on the differences between the quantities and cap ac-
ity levels of both firms. More precisely, in the quantity-setting competition, when th e price-raising effect is sufficiently
strong, both firms choose under-capacity, whereas when such an effect is sufficiently weak, both firms choose over-
capacity. Furthermore, in the price-setting competition, when the price-raising effect is sufficiently strong, both firms
choose over-capacity, whereas when such an effect is sufficiently weak, both firms choose under-capacity. Therefore,
the presence of the price-raisin g effect as the unilateral externality strikingly change s the difference between each firm’s
quantity and cap acity level in the contexts of both the quantity-setting competition and the price competitio n in a private
duopoly wi t h differenti a t e d go ods.
Keywords: Private Duopoly; Externality; Capacity Choice
1. Introduction
This paper considers the capacity choices of two profit-
maximizer firms in a private duopoly with unilateral ex-
ternality. More precisely, in the contexts of both quan-
tity-setting competition and price-setting competition
wherein one firm has a price-raising effect on the price
level of the product of the opponent firm as the unilateral
externality, we investigate the difference between the
quantity and capacity level of each firm. We introduce
the price-raising effect as the unilateral externality into
each firm’s demand function à la Choi and Lu [1]. The
purpose of this paper is to check the robustness of the
result on the difference between each firm’s quantity and
capacity level obtained in the standard private duopoly
with differentiated goods against the introduction of the
price-raising effect of the one firm’s product on the price
level of the opponent firm’s product in the fashion of
Choi and Lu [1].
In the model of this paper, following the model em-
ployed in Choi and Lu [1], we consider the situation
where both firms produce a homogeneous good if there
does not exist the price-raising effect of the product of
the one firm as the unilateral externality1. Similar to Choi
and Lu [1], since only the quantity of the product of the
one firm (say firm 1) has the price-raising effect on the
price level of the opponent firm’s product, we refer to
this effect as the unilateral externality. When the price-
raising effect of firm 1’s product is sufficiently strong, its
product becomes a complement to the product of the firm
without the price-raising effect (say firm 0). Hence, when
the price-raising of firm 1’s product as the unilateral
externality is sufficiently strong, the strategic relations
between the quantities/price levels and between the
capacity levels as the strategic variables of both firms are
changed in the context of both the quantity-setting com-
petition and the price-setting competition. Cabral and
Majure [2] found theoretical and empirical evidence on
the asymmetry of the strategic relation in the Portuguese
banking industry. More precisely, they indicated that for
some banks, the number of branches of rival banks is a
1As indicated in Choi and Lu [1], although we can investigate the
model such that the products of both firms can be differentiated even i
f
there is the price-raising effect of the one firm as the unilateral exter-
nality, such an assumption does not change the qualitative results ob-
tained in this paper.
*We are grateful for the financial support of KAKENHI (25870113).
All remaining errors a re our own.
C
opyright © 2013 SciRes. TEL
Y. NAKAMURA 203
strategic complement, whereas for other banks, it is a
strategic substitute2. By considering a standard oligopoli-
stic market without unilateral externality, Bulow et al. [3]
and Bulow et al. [4] found that the dominant firm in an
industry can consider the products of fringe firms as
strategic complements, whereas the fringe firms can con-
sider the output level of the dominant firm as strategic
substitutes. In addition, Tombak [5] considered a two-
stage game in which one firm regards its rival’s second-
stage strategic variable as a strategic complement where-
as the other firm regards its rival’s second-stage strategic
variable as a strategic substitu te3.
In contrast to the works in this field including Choi
and Lu [1], in this paper, we elaborate on the influences
of the price-raising effect that the dominant firm has on
not only the strategic variables in the market but also the
additional strategies (the cap acity levels) of the dominant
firm and the fringe firm, that is, whether the over-
capacity or under-capacity is achieved in both firms4.
In this paper, we show that when the price-raising
effect of the one firm’s product on the price level of the
other firm’s product is sufficiently strong, in the quan-
tity-setting competition, both firms choose under-capa-
city, while in the price-setting competition, both firms
choose over-capacity. These results sharply contrast with
those obtained in th e standard quantity-setting and price-
setting competitions with differentiated goods and with-
out the price-raising effect5. As described above, the
strength of the price-raising effect of firm 1’s product
changes the strategic relation between the strategic va-
riables of both firms, i.e., their quantities/price levels and
capacity levels. More precisely, when the price-raising
effect of the product of firm 1 is sufficiently strong
(weak), in the quantity-setting competition, the strategic
relation of firm 0’s quantity with firm 1’s quantity is a
strategic complement (substitute) in firm 0’s reaction
function in the q uantity-setting stag e6. On the other hand,
in the price-setting competition, when the price-raising
effect of the product of firm 1 is sufficiently strong
(weak), the strategic relation of firm 0’s price level with
firm 1’s price level is a strategic substitute (co mplement)
in firm 0’s reaction function in the price-setting stage7.
Furthermore, in the contexts of both quantity-setting
competition and price-setting compe-tition, the influence
of firm 1’s capacity level on firm 0’s quantity/price level
is changed when the price-raising effect is sufficiently
strong. Thus, when the price-raising effect is sufficiently
strong, the changes of the strategic relations between the
strategic variables yield changes of the signs of the dif-
ferences between the quantities and capacity levels of
both firms in the context of both quan tity-setting compe-
tition and the price-setting competition.
The remainder of this paper is organized as follows. In
Section 2, we formulate a private duopolistic model with
the prise-raising effect of the one firm’s product as the
unilateral externality and with the capacity choices of
both firms that will be investigated throughout th is paper.
In Section 3, from the viewpoints of quantity-setting
competition and the price-setting competition, we con-
sider the differences between the quantities and capacity
levels of both firms using the model built in Section 2.
Section 4 concludes with several remarks. The market
outcomes including each firm’s equilibrium price level
and profit are relegated to the appendix.
2. Model
Following Choi and Lu [1], we formulate an asymmetric
duopolistic model with unilateral externality wherein
both firms determine not only their quantities/pr ice levels
but also their capacity levels. The products are perfect
substitutes if the unilateral externality does not exist.
When the unilateral externality is introduced, the quan-
tity of firm 1’s products can have an price-raising effect
on the price level of firm 0’s products. On the basis of
Choi and Lu [1], we call the effect such that the output
level of firm 1 can raise firm 0’s price level the “uni-
lateral externality”. The inverse demand functions of
firms 0 and 1 are given as follows:
2The findings obtained in Cabral and Majure [2] are explained by the
following two facts: i) the geographic differences (urban or rural areas)
of the expansion patterns of incumbents (public banks) and entrants
(private banks) and ii) the degree of customer honesty (in general, rural
customers are more honest than urban customers) .
3More precisely, Tombak [5] investigated the situation where only the
dominant firm decid e s t h e in v e s tment for R&D in the first stage.
4By taking into account the managerial delegation in the fashion o
f
Fershtman and Judd [6], Sklivas [7], and Vickers [8], although Choi
and Lu [1] investigated the multi-stage game where the delegation
p
arameters of both the firms as well as their quantities/price levels are
determined, their main focus was to derive the result on the equilibrium
timing of setting th e quantities of both firms obtained in the endogenous
timing game (the consequent order of the game). We consider how the
setting of the strategic variable for the firm without the price-raising
effect except for its strategic variable in the market is influenced by the
setting of the strategic variables for the firm with the price-raising effect
as the unilateral externality.
5In the appendix, we give the results on the differences in the quantities
and capacity levels between both firms in the standard quantity-setting
and price-setting competitions with differentiated goods and without the
p
rice-raising effect. More precisely, in a standard quantity-setting com-
p
etition, both firms always choose ove
r
-capacity irrespective of the
degree of product differentiation, whereas in a standard price-setting
competition, both firms choose under-capacity irrespective of the de-
gree of product differentiation.

0011 01
1,, respectively,paq qpaqq
 
where i and i denote firm ’s price level and out-
put level, respectively, and parameter
p qi
measures the
6In firm 1’s reaction function in the quantity-setting competition, the
strategic relation of firm 1’s quantity with firm 0’s quantity is a strate-
gic substitute irrespective of the strength of the price-raising effect o
f
firm 1.
7In firm 1’s reaction function in the price-setting competition, the strategic
relation of firm 1’s price level with firm 0’s price level is a strategic
complement irrespective of the strength of price-raising effect of firm 1.
Copyright © 2013 SciRes. TEL
Y. NAKAMURA
204
degree of the price-raising effect as the unilateral exter-
nality, . Note that denotes the demand para-
meter and 8. indicates that
the price-raising effect of firm 1’s output level is rela-
tively strong whereas indicates that the price-
raising effect of firm 1’s output level is relatively weak.
Futhermore, implies that firm 1’s product
becomes a complement to firm 0’s product whereas
implies that firm 1’s product becomes a
substitute for firm 0’s product.
0,1i
1
a
0,1
i

0,1 1,2

1,2
,
ii
Cqx
1,2
0,
Both firms adopt identical technologies represented by
the cost function , where i
x
is the capacity
level of firm , . Following Vives [9], Ogawa
[10], Bárcena-Ruiz and Garzón [11], Tomaru et al. [12],
Nakamura and Saito [13], Nakamura and Saito [14], and
Nakamura [15], we assume that the cost function is given
by iii , . This cost
function implies that if each firm’s output level equals its
capacity level, ii
, the long-run average cost is
minimized. The profit of firm is given by
.
i

,
iii
Cqx
pqCq
0,1i
mq q
qx

,xi
2
x

0,1
0,1i
i
iiiiii
We investigate the game with the following orders of
each firm’s moves: In the first stage, firms 0 and 1
simultaneously set their capacity levels. In the second
stage, after both firms observe their capacity levels, they
engage in either quantity-setting competition or price-
setting competition with each other.

3. Equilibrium Analysis
3.1. Quantity Competition
We first solve the quantity-setting game by backward
induction from the second stage to obtain the subgame
perfect Nash equilibrium. In the second stage, firm
maximizes its profit i with respect to i, i
q
0,1i.
The best response functions of firms 0 and 1 in the
second stage are given as follows:
 
01
qq 01
;,xx a

1 0
2qx
14,q
m (1)
10
qq
q
1
q
q
1
;x a 0
q1
x24.m
(2)
From Equations (1) and (2), when , 0 is
decreasing in 1, whereas when , is in-
creasing in . For any , 1 is de-
creasing in 0. Thus, the strategic relation of the quan-
tity of firm 0 with the quantity of firm 1 strictly depends
on the value of

0,1

1,2 0
q

1,2q
q

10,
; that is, when , the quantity
of firm 0 is a strategic substitute for the quantity of firm
1, whereas when , the quantity of firm 0 is a
strategic complement to the quantity of firm 1. On the
other hand, the strategic relation of the quantity of firm 1
is a strategic substitute for the quantity of firm 0
irrespective of

0,1
1,2
0,1 1,2
.
Furthermore, we obtain the following equilibrium
quantities of firms 0 and 1 as the functions of their capa-
city levels in the Nash equilibrium in the quantity-setting
stage:

011
822
15
xxxa
0
33 ,
m
q

 
 
(3)
0
32
.
15
amx x
 
1
1
8
q (4)
In the first stage, firms 0 and 1 realize that the choices
of their capacity levels influence their quantity deter-
mined in the second stage. Provided Equations (3) and
(4), respectively, firms 0 and 1 simultaneously and in-
dependently set their cap acity levels with respect to their
profits. Thus, by solving the first-order conditions of the
profits of firms 0 an d 1 , we o btain

  
1
16 213
97 30
xa
01 2
3,
m
xx


 
 (5)

0
2
16 332
97 30
amx



10 ,
xx (6)
yielding

 
2
023
123
18 ,
5
3.
5
q
q
x
x




16 13
559 4194
16 13
559 4194
am
am



Note that superscript is used to represent the
subgame perfect Nash equilibrium market outcomes in
the quantity-setting competition. Then, the equilibrium
quantities of firms 0 and 1 are given as follows:
q

 
2
023
123
1513 18,
559 41945
1513 3.
559 41945
q
q
am
q
am
q








Therefore, from easy calculations, we obtain the
following equilibrium result on the differences between
the quantities and capacity levels of firms 0 and 1:


2
00 23
11 23
11318,
559 41945
1133.
559 41945
qq
qq
am
qx
am
qx





 

 
Proposition 1 In the quantity-setting competition,
when the price-raising effect of firm 1’s product on the
price level of firm 0’s product is sufficiently strong, i.e.,
1,2
, both firms 0 and 1 choose under-capacity. In
contrast, in the quantity-setting competitio n, when such a
price-raising effect of firm 1’s product is sufficiently
8Similar to Choi and Lu [1], we omit the case of 1
since firm 0’s
p
rice level is independent of firm 1’ s output level; this is a trivial case.
Copyright © 2013 SciRes. TEL
Y. NAKAMURA 205
weak, i.e., , both firms 0 and 1 choose over-
capacity.
0,1
,0,ij

0,1
i
Proposition 1 indicates that whether either of the two
firms has a price-raising effect on the price level of the
product of its opponent firm strictly determines the
differences between the quantities and capacity levels of
both firms. More precisely, when the price-raising effect
of the one firm’s product on the price level of the product
of its opponent firm is sufficiently strong, both firms
choose under-capacity, whereas when such an effect is
sufficiently weak, both choose over-capacity. This result
is strikingly different from that obtained in the standard
quantity-setting competition with differentiated goods9.
In the standard private duopolistic competition without
the price-raising effect, since firm i pays attention to its
market share in order to increase its profit, it attempts to
decrease the quantity of its opponent firm j n order to
increase its market share by increasing its capacity level
when the relation between their output levels is sub-
stitutable, . In addition, in the case
wherein the relation between the products of both firms
is complementary, firm i has an incentive to increase its
market share by decreasing the quantity of its opponent
firm j by decreasing its own capacity, and thus, this
behavior of decreasing firm ’s capacity also decreases
firm j’s capacity since their capacity levels are strategic
complements in the first stage,
.
Although the capacity levels of both firms tend to be low,
their quantities are lower than their capacity levels since
their capacity levels are positively associated with their
own quantities. Thus, irrespectiv e of whether the relation
of the goods produced by both firms are substitutable or
complementary, in a standard quantity-setting duopoly
without the price-raising effect, they choose over-
capacity.
1;i j
i
,0,1;
i jij
In the quantity-setting competition wherein the one
firm has the price-raising effect of its product on the
price level of the product of the other firm, if such an
effect is sufficiently weak, i.e., , the intuition
behind the result that both firms 0 and 1 choose over-
capacity is similar to that given in the standard quantity-
setting competition with substitutable goods and without
the price-raising effect10. From Equations (3) and (4),
when , both firms 0 and 1 have incentive to
decrease the quantities of their respective op ponent firms
through increasing their own capacity in order to expand
their respective market share, implying that both firms
choose over-capacity. On the other hand, when the
price-raising effect of firm 1’s product is sufficiently
strong, i.e.,
0,1
1,2
, we obtain the result that the diffe-
rences between the quan tities and capacity lev els of firms
0 and 1 are positive, which is strikingly different from
the results obtained for i) the quantity-setting com-
petition without the price-raising effect and ii) the case
wherein such a price-raising effect is sufficiently weak,
i.e.,
10,
. The intuition behind this result is as
follows: from Equation (3), firm 1 which has the price-
raising effect has an incentive to decrease firm 0’s quan-
tity by decreasing its own capacity, and consequently,
firm 1 chooses under-capacity. On the other hand, from
Equation (4), firm 0, which does not have the price-
raising effect has an incentive to decrease firm 1’s quan-
tity by increasing its own capacity, similar to the case
where
0,1
. However, taking Equations (5) and (6)
into account, firm 0’s capacity tends not to become so
high when
1,2
. Therefore, since the quantity of
firm 1 does not become so low because of the relatively
low capacity of firm 0, from Equation (1), the quantity of
firm 0 is higher relative to its capacity when
1,2
i

0, 1
.
Consequently, firm 0 also chooses under-capacity. We
emphasize that the strength of the price-raising effect and
the change of the relation of the goods produced by firms
0 and 1 on the basis of such an effect determine the
difference between the quantity and capacity of each firm
in the quantity-setting competition with the price-raising
effect as the unilateral effect.
3.2. Price Competition
We next solve the price-setting game by backward
induction from the second stage to obtain the subgame
perfect Nash equilibrium. In the second stage, firm
maximizes its profit with respect to i, . The
best-response functions of firms 0 and 1 in the second
stage are given as follows:
pi


2
10
22
21
pmx
 

2
,
a



0
p (7)

001
2
.
p x
1
p2
21
pm


(8)
From Equations (7) and (8), when , 0 is
increasing in , whereas when , 0 is de-
creasing in . For any , 1 is
increasing in 0. Thus, the strategic relation of the price
level of firm 0 with the price level of firm 1 strictly
depends on the value of

0,1

1,2 p

1,2
p
p
1
p
1
p
p

0, 1
; that is, when
10,
, the
strategic relation of the price level of firm 0 is a strategic
complement to the price level of firm 1, whereas when
1,2
, the strategic relation of the price level of firm
0 is a strategic substitute for the price level of firm 1. On
9This results on the differences between the quantities and capacity
levels of firms 0 and 1, which are obtained in the standard quantity-
setting competition with differentiated goods and without the price-
raising effect, are given in the appendix. More concretely, in both cases
wherein firms 0 and 1 produce substitutable goods or complementary
goods, it was shown that they both always choose over-capacity.
10As described in the setting of this model, we recall that the fact that
the price-raising effect is sufficiently weak implies that the products
firms 0 and 1 are substitutable.
Copyright © 2013 SciRes. TEL
Y. NAKAMURA
Copyright © 2013 SciRes. TEL
206
Furthermore, we obtain the following price levels of
firms 0 and 1 as the functions of th e capacity lev els in th e
Nash equilibrium in the price-setting stage.
the other hand, the strategic relation of the price level of
firm 1 is a strategic complement to the price level of firm
0 irrespective of .

0,1 1,2
22
010112
2
444224223,
87
xxxxx ma
 



0
p (9)

2
10
2
2432212
.
87
am xx
 

 

1
p (10)
In the first stage, firms 0 and 1 realize that the choices
of their capacity levels influence their price levels in the
second stage. Provided Equations (9) and (10), re-
spectively, firms 0 and 1 set their capacity levels with re-
spect to their profits. Thus, by solving the first-order
conditions of the profits of firms 0 and 1 in the first stage,
we obtain

1
01 234
43 4111,
28 523710
xam
xx
 
 
 
  (11)

20
10 234
234222
,
28 523710
xa m
xx
 
 
 
  (12)
yielding

2
23
41
360 231
am 23
0456
6178 ,
80 2647513
p
x



 




2345
123
212344
360 231

456
3299.
80 26475 13
pam
x


 
 





Note that superscript p represents the subgame perfect
Nash equilibrium market outcomes in the price-setting
competition. Then, the equilibrium quantities of firms 0
and 1 are given as follow s:
22
0
3
456
276 ,
80 2647513
p
q

23
287
360 231
am



 





22
1
3
456
46 5
80 2647513
pam
q
 
23
87
360 231



 




Therefore, from easy calculations, we obtain the
following equilibrium result on the differences between
the quantities and capacity levels of firms 0 and 1:
 

00
2
23
211
360 231

456
225 ,
80 2647513
pp
qx
am
 


 





11
23
23
12
360 231

456
465 .
80 2647513
pp
qx
am



 



Proposition 2 In the price-setting competition, when
the price-raising effect of firm 1’s product on the price
level of firm 0’s product is sufficiently strong, i.e.,
1,2
, both firms 0 and 1 choose over-capacity. In
contrast, when such a price-raising effect of firm 1’s
product is sufficiently weak, i.e., , both firms 0
and 1 choose under-capacity.
0,1
Similar to the quantity-setting competition with the
price-raising effect of the product of firm 1, Proposotion
2 indicates that the differences between the quantities
and capacity levels of firms 0 and 1 strictly depend on
the strength of the price-raising effect o f firm 1’s product
on the price level of firm 0’s product. More concretely, it
is shown that when the price-raising effect of firm 1’s
product is sufficiently strong, the differences between the
quantities and capacity levels of firms 0 and 1 are ne-
gative, whereas when su ch an effect is sufficiently weak,
the differences between their quantities and capacity
levels are positive11.
In the price-setting competition with the price-raising
effect, when such an effect is sufficiently weak, i.e.,
0,1
from Equations (9) and (10), both firms 0 and
1 attempt to decrease the quantity of their respective
opponent firm by decreasing their capacity in order to
expand their own market share. Thus, when
0,1
,
both firms 0 and 1 choose under-capacity, which is the
same result as that obtained in the standard price-setting
competition with differentiated goods and without the
11These results on the differences between the quantities and capacity
levels of firms 0 and 1, which are obtained in the standard price-setting
competition with differentiated goods and without the price-raising
effect, are given in the appendix. More concretely, in both cases
wherein firms 0 and 1 produce substitutable goods or complementary
goods with each other, it is shown that they always choose under-
capacity together.
Y. NAKAMURA 207
price-raising effect12.
In contrast, the intuition behind the result that both
firms 0 and 1 choose over-capacity in the price-setting
competition when is given as follows: from
Equation (9), firm 1 which has the price-raising effect
attempts to increase firm 0’s price level by setting its
capacity level high in order to decrease the quantity of
firm 0, implying that it chooses over-capacity. Further-
more, similar to the case wherein , from Equ-
ation (10), firm 0 tends to decrease its own capacity level
in order to decrease firm 1’s quantity by increasing the
price level of firm 1 when as well. However,
taking Equations (11) and (12) into account, firm 0’s
capacity level tends not to become low when
1,2

0,1
2
1,
1,2
.
Therefore, since the price level of firm 1 does not be-
come so high because of the relatively high capacity
level of firm 0, from Equation (7), the price of firm 0
becomes relatively high, Consequently, since the quan-
tity of firm 0 becomes low, firm 0 also chooses over-
capacity when .

1,2
For both the quantity-setting competition with the
price-raising effect and the pr ice-setting co mp etition with
the price-raising effect, we find that the choices of the
quantity/price level and the capacity level for the firm
with the price-raising effect influences not only th e selec-
tion of the quantity/price level for its opponent firm in
the market, but also the selection of the capacity level fo r
its opponent firm. These choices change the differences
between the quantities and capacity levels of the two
firm.
4. Conclusions
This paper investigated the differences between the out-
put and capacity levels in a private duopoly composed of
two profit-maximizer firms in both quantity-setting co m-
petition and price-setting competition, particularly when
one firm has the price-raising effect on the price level of
the product of its opponent firm as the unilateral exter-
nality. In both the standard quantity-setting competition
and price-setting competition with differentiated goods
and without the price-raising effect, the differences be-
tween the quantity and capacity levels of the two firms
do not depend on the relation between their products, that
is, whether they are substitutable or complementary.
More precisely, in the standard quantity-setting competi-
tion with differentiated goods, bo th firms 0 and 1 always
choose over-capacity, whereas in the standard price-
setting competition with differentiated goods, they al-
ways choose under-capacity. In contrast, in the private
duopoly with the price-raising effect of th e produ ct of th e
one firm, the differences between the quantities and
capacity levels of both firms strictly depend on the
strength of such an effect in not only the quantity-setting
competition but also the price-setting competition. In
particular, when the price-raising effect is sufficiently
strong, both firms choose under-capacity in the quantity-
setting competition whereas they both choose over-capa-
city in the price-setting competition. In the model of this
paper, in the quantity-setting and price-setting com-
petitions when the price-raising effect of the one firm is
sufficiently strong, the product of the firm with such an
effect is a complement to the product of the firm without
such an effect, while the product of the firm without such
an effect is always a substitute for the product of th e firm
with such an effect. Thus, the change of the strategic
relation between the quantities/price levels and capacity
levels of both firms along with the change of the relation
of the product of the firm that has the price-raising effect
as the unilateral externality with the product of the firm
without such an effect (i.e., substitutable or comple-
mentary) strikingly influences the differences between
their quantities and capacity levels even if their strategic
variables ( or ) are fixed in the market. The above
findings comprise the most important contribution of this
paper.
q p
Finally, we mention an issue to be addressed in the
future. Throughout this paper, we explored the diffe-
rences between the quantity and capacity level of each
firm by adopting the private duopolistic model with the
unilateral externality à la Choi and Lu [1]. However, we
did not consider the impact of the separation between
ownership and management, which was investigated in
Choi and Lu [1], on the differen ce between the quantities
and capacity levels of the firms13. Future research must
deal with the above problems.
12In the standard price-setting duopoly with differentiated goods,when
the goods produced by both firms are substitutable, since each firm’s
capacity is negatively associated with the opponent firm’s price level,
each attempts to decrease the quantity of its opponent firm by increas-
ing its opponent firm’s price level by decreasing its own capacity level
in order to increase its own market share, and hence, each firm’s quan-
tity is relatively higher than its capacity level. Thus, bo th firms choose
under-capacity. On the other hand,when the relation between the
p
roducts of the firms is complementary, each firm has an incentive to
increase its opponent firm’s price level by increasing its capacity level
in order to increase its market share, and thus, such capacity-increasing
behavior also increases its opponent firm’s capacity since the capacity
levels of both firms are strategic complements in the first stage. Al-
though the capacity levels of both firms tend to become high,thei
r
quantities are higher than their capacity levels since their capacity lev-
els are negatively associated with their own price levels. Thus,whether
the relation of the goods produced by both firms is substitutable or
complementary, in a standard price-setting duopoly without the
p
rice-raising effect, they choose under-capacity.
13Several types of strategic delegation, along with the separation be-
tween ownership and management, are presented as the objective func-
tions of managers on the basis of the manager’s bonus. For instances,
Jansen et al. [16] introduced the weighted sum of the firm’s profit and
its market share as the objective function of its manager, and Miller and
Pazgal [17] and Miller and Pazgal [18] considered the weighted sum o
f
the firm’s profit and (the sum of) t h e pr of i t (s) of its opponent f i r m(s).
Copyright © 2013 SciRes. TEL
Y. NAKAMURA
Copyright © 2013 SciRes. TEL
208
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Y. NAKAMURA 209
Appendix
Equilibrium Outcomes in a Standard
Quantity-Setting Competition with
Differentiated Goods
In this appendix, we formulate a standard private quan-
tity-setting competition with differentiated goods wherein
firms 0 and 1 choose not only their ou tput levels but also
their capacity levels. It is assumed that the inverse
demand functions of firms 0 and 1 are 00
and 101
, respectively. Note that and
denote the demand parameter and the degree of product
differentiation, respectively. Moreover, similar to the
setting on the cost functions of firms 0 and 1 in the main
body of this paper, their cost functions are represented as
i,
1
paqbq 
abpabqq 
 
;
iiiii
xmq q
2
Cq x
0, 1i. Then, in the
standard quantity-setting competition without the price-
raising effect, we obtain the following equilibrium quan-
tities and capacity levels of firms 0 and 1:



2
23
23
16 ,
32 164
16 ,
32 164
0,1.
i
i
bam
qbbb
am
xbbb
i



Note that superscrip t * is u sed to deno te the e quilibr ium
market outcomes in the standard quantity-setting com-
petition without the price-raising effect.
Then we obtain the following equilibrium differences
between the quantities an d capacity levels of firms 0 and
1:

2
23
0,
32 164
1, 00,1,
0,1.
ii
bam
qx bbb
b
i




Thus, we find that in the standard quantity-setting
competition with differentiated goods and without the
price-raising effect, firms 0 and 1 both choose over-
capacity irrespective of the relation between the pro-
ducts.
Equilibrium Outcomes in a Standard
Price-Setting Competition with Differentiated
Goods
Similar to the standard quantity-setting competition with-
out the price-raising effect, in the price-setting com-
petition without the price raising effect, we give the
following equilibrium outcomes including the quantities
and capacity levels of firms 0 and 1:



24
23456
24
23456
16 9,
32 162899
28 6,
321628 9 9
0,1.
i
i
bbam
qbbbbbb
bbam
xbbbbbb
i


 
 
 
 
Note that superscript ** is used to denote the equilib-
rium market outcomes in the standard quantity-setting
competition without the price-raising effect.
Thus, we obtain the following equilibrium differences
between the quantities an d capacity levels of both firms:


22
23456
30,
32 162899
1,00,1 ,0,1.
ii
bbam
qx bbbbbb
bi
 

 
 
Thus, in the standard price-setting co mpetition without
the price-raising effect, we find that both firms 0 and 1
choose under-capacity irrespective of the relation be-
tween the products.
Equilibrium Outcomes of Firms 0 and 1 in
Quantity-Setting Competition
In this subsection, we give the equilibrium following
market outcomes, including the equilibrium price levels
and profits of both firms 0 and 1 in the quantity-setting
competition with the price-raising effect as the unilateral
externality:
 
0
232 3
23
2195 7311169 273673
559 41945
q
p
ma
 

 


223
123
13 339034136,
559 41945
qam
p


 


 

 


2
222
02
23
22 2
12
23
213189730
,
559 41945
21339730
.
559 41945
q
q
am
am
 



 
 
 
 
Equilibrium Outcomes of Firms 0 and 1 in
Price-Setting Competition
In this subsection, we give the equilibrium following
market outcomes, including the equilibrium price levels
and profits of both firms 0 and 1 in the price-setting
competition with the price-raising effect as the unilateral
externality:
Copyright © 2013 SciRes. TEL
Y. NAKAMURA
Copyright © 2013 SciRes. TEL
210

23456 23456
023456
6418420877 11 9284076774311,
80 2643602317513
pma
p
 
 
 
 
 
2
23234 5
123456
4 6564 216284163383,
80 2643602317513
pam
p
 
 
 
 



2
23 22
02
23456
412528 523710,
80 2643602317513
pam
 
 

  
34



2
2232345
12
23456
46 52880 894711.
80 2643602317513
pam
 
 

  