Download EC 170: Industrial Organization

Product Variety and Quality
under Monopoly
Chapter 7: Product Variety and
Quality under Monopoly
1
Introduction
• Most firms sell more than one product
• Products are differentiated in different ways
– horizontally
• goods of similar quality targeted at consumers of
different types
– how is variety determined?
– is there too much variety
– vertically
• consumers agree on quality
• differ on willingness to pay for quality
– how is quality of goods being offered determined?
Chapter 7: Product Variety and
Quality under Monopoly
2
Horizontal product differentiation
• Suppose that consumers differ in their tastes
– firm has to decide how best to serve different types of
consumer
– offer products with different characteristics but similar
qualities
• This is horizontal product differentiation
– firm designs products that appeal to different types of
consumer
– products are of (roughly) similar quality
• Questions:
– how many products?
– of what type?
– how do we model this problem?
Chapter 7: Product Variety and
Quality under Monopoly
3
A spatial approach to product variety
• The spatial model (Hotelling) is useful to
consider
– pricing
– design
– variety
• Has a much richer application as a model of
product differentiation
– “location” can be thought of in
• space (geography)
• time (departure times of planes, buses, trains)
• product characteristics (design and variety)
– consumers prefer products that are “close” to their
preferred types in space, or time or characteristics
Chapter 7: Product Variety and
Quality under Monopoly
4
An geographic example of product variety
McDonald’s
Burger King
Wendy’s
Chapter 7: Product Variety and
Quality under Monopoly
5
A Spatial approach to product variety 2
• Assume N consumers living equally spaced along Main
Street – 1 mile long.
• Monopolist must decide how best to supply these
consumers
• Consumers buy exactly one unit provided that price
plus transport costs is less than V.
• Consumers incur there-and-back transport costs of t
per mile
• The monopolist operates one shop
– reasonable to expect that this is located at the center of Main
Street
Chapter 7: Product Variety and
Quality under Monopoly
6
Suppose that the monopolist
The spatial model
Price
sets a price ofPrice
p1
p1 + tx
p1 + t.x
V
V
All consumers within
distance x1 to the left
and right of the shop
will by the product
z=0
t
t
p1
x1
1/2
What determines
x1?
x1
z=1
Shop 1
p1 + tx1 = V, so x1 = (V – p1)/t
Chapter 7: Product Variety and
Quality under Monopoly
7
The spatial model
Price
p1 + t.x
Suppose the firm
2reduces the price
Price
p1 +tot.xp2?
V
V
Then all consumers
within distance x2
of the shop will buy
from the firm
z=0
p1
p2
x2
x1
1/2
x1
x2
z=1
Shop 1
Chapter 7: Product Variety and
Quality under Monopoly
8
The spatial model 3
• Suppose that all consumers are to be served at price p.
– The highest price is that charged to the consumers at the ends of
the market
– Their transport costs are t/2 : since they travel ½ mile to the shop
– So they pay p + t/2 which must be no greater than V.
– So p = V – t/2.
• Suppose that marginal costs are c per unit.
• Suppose also that a shop has set-up costs of F.
• Then profit is p(N, 1) = N(V – t/2 – c) – F.
Chapter 7: Product Variety and
Quality under Monopoly
9
Monopoly pricing in the spatial model
• What if there are two shops?
• The monopolist will coordinate prices at the two shops
• With identical costs and symmetric locations, these prices
will be equal: p1 = p2 = p
– Where should they be located?
– What is the optimal price p*?
Chapter 7: Product Variety and
Quality under Monopoly
10
Location with two shops
Delivered price to
Suppose that the entire market is
Price
If there are two shops
they will be located
V
symmetrically a
distance d from the
The
maximumofprice
end-points
the p(d)
the firmmarket
can charge
is determined
Now raisebythethe
price
consumers
at the
at each
shop
Start
with
a
low
center of the marketprice
at each shop
Suppose that
d < 1/4
z=0
consumers at the
tomarket
be served
center equals
their reservation price Price
V
p(d)
What determines
p(d)?
d
Shop 1
1/2
1-d
Shop 2
z=1
The shops should be
moved inwards
Chapter 7: Product Variety and
Quality under Monopoly
11
Delivered price to
consumers at the
end-points equals
their reservation price
Location with two shops 2
The maximum price
the firm can charge
is now determined
by the consumers
at the end-points
of the market
Price
Price
V
V
p(d)
p(d)
Now raise the price
at each shop
Start with a low price
at each shop
Now suppose that
d > 1/4
Now what
determines p(d)?
z=0
d
Shop 1
1/2
1-d
Shop 2
z=1
The shops should be
moved outwards
Chapter 7: Product Variety and
Quality under Monopoly
12
It follows that Location
shop 1 should
be located at
Price
1/4 and shop 2
at 3/4
with two shops 3
Price at each
shop is then
p* = V - t/4
Price
V
V
V - t/4
V - t/4
Profit at each shop
is given by the
shaded area
c
c
z=0
1/4
Shop 1
1/2
3/4
Shop 2
z=1
Profit is now p(N, 2) = N(V - t/4 - c) – 2F
Chapter 7: Product Variety and
Quality under Monopoly
13
Three shops
What if there
are three shops?
By the same argument
they should be located
at 1/6, 1/2 and 5/6
Price
Price
V
Price at each
shop is now
V - t/6
V
V - t/6
z=0
V - t/6
1/6
Shop 1
1/2
Shop 2
5/6
z=1
Shop 3
Profit is now p(N, 3) = N(V - t/6 - c) – 3F
Chapter 7: Product Variety and
Quality under Monopoly
14
Optimal number of shops
• A consistent pattern is emerging.
• Assume that there are n shops.
• They will be symmetrically located distance 1/n apart.
• We have already considered n = 2 and n = 3. How many
shops should
• When n = 2 we have p(N, 2) = V - t/4
there be?
• When n = 3 we have p(N, 3) = V - t/6
• It follows that p(N, n) = V - t/2n
• Aggregate profit is then p(N, n) = N(V - t/2n - c) – nF
Chapter 7: Product Variety and
Quality under Monopoly
15
Optimal number of shops 2
Profit from n shops is p(N, n) = (V - t/2n - c)N - nF
and the profit from having n + 1 shops is:
p*(N, n+1) = (V - t/2(n + 1)-c)N - (n + 1)F
Adding the (n +1)th shop is profitable
if p(N,n+1) - p(N,n) > 0
This requires tN/2n - tN/2(n + 1) > F
which requires that n(n + 1) < tN/2F.
Chapter 7: Product Variety and
Quality under Monopoly
16
An example
Suppose that F = $50,000 , N = 5 million and t = $1
Then tN/2F = 50
For an additional shop to be profitable we need n(n + 1) < 50.
This is true for n < 6
There should be no more than seven shops in this case: if
n = 6 then adding one more shop is profitable.
But if n = 7 then adding another shop is unprofitable.
Chapter 7: Product Variety and
Quality under Monopoly
17
Some intuition
• What does the condition on n tell us?
• Simply, we should expect to find greater product variety
when:
– there are many consumers.
– set-up costs of increasing product variety are low.
– consumers have strong preferences over product characteristics
and differ in these
• consumers are unwilling to buy a product if it is not “very close”
to their most preferred product
Chapter 7: Product Variety and
Quality under Monopoly
18
How much of the market to supply
• Should the whole market be served?
– Suppose not. Then each shop has a local monopoly
– Each shop sells to consumers within distance r
– How is r determined?
•
•
•
•
•
•
•
it must be that p + tr = V so r = (V – p)/t
so total demand is 2N(V – p)/t
profit to each shop is then p = 2N(p – c)(V – p)/t – F
differentiate with respect to p and set to zero:
dp/dp = 2N(V – 2p + c)/t = 0
So the optimal price at each shop is p* = (V + c)/2
If all consumers are served price is p(N,n) = V – t/2n
– Only part of the market should be served if p(N,n)< p*
– This implies that V < c + t/n.
Chapter 7: Product Variety and
Quality under Monopoly
19
Partial market supply
• If c + t/n > V supply only part of the market and set
price p* = (V + c)/2
• If c + t/n < V supply the whole market and set price
p(N,n) = V – t/2n
• Supply only part of the market:
– if the consumer reservation price is low relative to marginal
production costs and transport costs
– if there are very few outlets
Chapter 7: Product Variety and
Quality under Monopoly
20
Are there too
Social optimum many shops or
What number of shops maximizes total surplus? too few?
Total surplus is consumer surplus plus profit
Consumer surplus is total willingness to pay minus total revenue
Profit is total revenue minus total cost
Total surplus is then total willingness to pay minus total costs
Total willingness to pay by consumers is N.V
Total surplus is therefore NV - Total Cost
So what is Total Cost?
Chapter 7: Product Variety and
Quality under Monopoly
21
Assume that
there
are n shops
Social optimum 2
Price
Price
Transport cost for
each shop is the area
V
of these two triangles
multiplied by
consumer density
V
Consider shop
i
Total cost is
total transport
cost plus set-up
costs
t/2n
z=0
t/2n
1/2n
1/2n
z=1
Shop i
This area is t/4n2
Chapter 7: Product Variety and
Quality under Monopoly
22
Social optimum 3
Total cost with n shops is, therefore: C(N,n) = n(t/4n2)N + nF
If =
t =tN/4n
$1, F+=nF
$50,000,
5 million then
this
Total cost with n + 1 shops is: C(N,n+1)N==tN/4(n+1)+
(n+1)F
condition
tells
There
should
beusfive shops:
Adding another shop is socially efficient if that
C(N,n
+ 1) << C(N,n)
n(n+1)
25 another
with n = 4 adding
This requires that tN/4n - tN/4(n+1) > F
shop is efficient
which implies that n(n + 1) < tN/4F
The monopolist operates too many shops and, more
generally, provides too much product variety
Chapter 7: Product Variety and
Quality under Monopoly
23
Product variety and price discrimination
• Suppose that the monopolist delivers the product.
– then it is possible to price discriminate
• What pricing policy to adopt?
–
–
–
–
charge every consumer his reservation price V
the firm pays the transport costs
this is uniform delivered pricing
it is discriminatory because price does not reflect costs
Chapter 7: Product Variety and
Quality under Monopoly
24
Product variety and price discrimination
• Suppose that the monopolist delivers the product.
– then it is possible to price discriminate
• What pricing policy to adopt?
–
–
–
–
charge every consumer his reservation price V
the firm pays the transport costs
this is uniform delivered pricing
it is discriminatory because price does not reflect costs
Chapter 7: Product Variety and
Quality under Monopoly
25
Product variety and price discrimination 2
• Should every consumer be supplied?
– suppose that there are n shops evenly spaced on Main Street
– cost to the most distant consumer is c + t/2n
– supply this consumer so long as V (revenue) > c + t/2n
• This is a weaker condition than without price
discrimination.
• Price discrimination allows more consumers to be
served.
Chapter 7: Product Variety and
Quality under Monopoly
26
Product variety & price discrimination 3
• How many shops should the monopolist operate now?
—Suppose that the monopolist has n shops and is supplying
the entire market.
—Total revenue minus production costs is NV – Nc
—Total transport costs plus set-up costs is C(N, n)=tN/4n + nF
—So profit is p(N,n) = NV – Nc – C(N,n)
—But then maximizing profit means minimizing C(N, n)
—The discriminating monopolist operates the socially
optimal number of shops.
Chapter 7: Product Variety and
Quality under Monopoly
27
Monopoly and product quality
• Firms can, and do, produce goods of different qualities
• Quality then is an important strategic variable
• The choice of product quality determined by its ability to
generate profit; attitude of consumers to q uality
• Consider a monopolist producing a single good
– what quality should it have?
– determined by consumer attitudes to quality
•
•
•
•
prefer high to low quality
willing to pay more for high quality
but this requires that the consumer recognizes quality
also some are willing to pay more than others for quality
Chapter 7: Product Variety and
Quality under Monopoly
28
Demand and quality
• We might think of individual demand as being of the form
– Qi = 1 if Pi < Ri(Z) and = 0 otherwise for each consumer i
– Each consumer buys exactly one unit so long as price is less
than her reservation price
– the reservation price is affected by product quality Z
• Assume that consumers vary in their reservation prices
• Then aggregate demand is of the form P = P(Q, Z)
• An increase in product quality increases demand
Chapter 7: Product Variety and
Quality under Monopoly
29
Demand and quality 2
Begin with a particular demand curve
for a good of quality Z1
Price
Then an increase in product
R1(Z2)
Suppose that
an from
increase
quality
Z1 toinZ2 rotates
P(Q, Z2)
quality the
increases
demandthe
curve around
If the price is P1willingness
and the product
quality
to pay of
the quantity
axis as follows
is
Z
then
all
consumers
with
reservation
1
inframarginal consumers more
P2
prices greater than
than P
the good
1 will
that
of buy
the marginal
R1(Z1)
Quantity Q1 can now be
consumer
This
is
the
These are the
P1
sold for the higher
marginal
inframarginal
price P2
consumer
consumers
P(Q, Z1)
Q1
Quantity
Chapter 7: Product Variety and
Quality under Monopoly
30
Demand and quality 3
Price
R1(Z1)
P2
P1
P(Q, Z1)
Q1
Suppose instead that an
Then anin
increase in product
increase
fromthe
Z1 to Z2 rotates
qualityquality
increases
thepay
demand
curve around
willingness to
of marginal
the price
axis as follows
consumers
more
than that of the inframarginal
consumers
Once again quantity Q1
can now be sold for a
higher price P2
P(Q, Z2)
Quantity
Chapter 7: Product Variety and
Quality under Monopoly
31
Demand and quality 4
• The monopolist must choose both
– price (or quantity)
– quality
• Two profit-maximizing rules
– marginal revenue equals marginal cost on the last unit sold for
a given quality
– marginal revenue from increased quality equals marginal cost
of increased quality for a given quantity
• This can be illustrated with a simple example:
P = Z( - Q) where Z is an index of quality
Chapter 7: Product Variety and
Quality under Monopoly
32
Demand and quality 5
P = Z( - Q)
Assume that marginal cost of output is zero: MC(Q) = 0
Cost of quality is C(Z) = aZ2
Marginal cost of quality = dC(Z)/d(Z)
= 2aZ
The firm’s profit is:
This means that quality
costly and becomes
increasingly costly
p(Q, Z) =PQ - C(Z) = Z( - Q)Q - aZ2
Chapter 7: Product Variety and
Quality under Monopoly
33
Demand and quality 6
Again, profit is:
p(Q, Z) =PQ - C(Z) = Z( - Q)Q - aZ2
The firm chooses Q and Z to maximize profit.
Take the choice of quantity first: this is easiest.
Marginal revenue = MR = Z - 2ZQ
MR = MC  Z - 2ZQ = 0  Q* = /2
 P* = Z/2
Chapter 7: Product Variety and
Quality under Monopoly
34
Demand and quality 7
Total revenue = P*Q* = (Z/2)x(/2) = Z2/4
So marginal revenue from increased quality is
MR(Z) = 2/4
Marginal cost of quality is
MC(Z) = 2aZ
Equating MR(Z) = MC(Z) then gives
Z* = 2/8a
Does the monopolist produce too high or too low quality?
Chapter 7: Product Variety and
Quality under Monopoly
35
Demand and quality: multiple products
• What if the firm chooses to offer more than one
product?
– what qualities should be offered?
– how should they be priced?
• Determined by costs and consumer demand
Chapter 7: Product Variety and
Quality under Monopoly
36
Demand and quality: multiple products 2
• An example:
– two types of consumer
– each buys exactly one unit provided that consumer surplus is
nonnegative
– if there is a choice, buy the product offering the larger
consumer surplus
– types of consumer distinguished by willingness to pay for
quality
• This is vertical product differentiation
Chapter 7: Product Variety and
Quality under Monopoly
37
Vertical differentiation
• Indirect utility to a consumer of type i from consuming a
product of quality z at price p is Vi = i(z – zi) – p
– where i measures willingness to pay for quality;
– zi is the lower bound on quality below which consumer type i will
not buy
– assume 1 > 2: type 1 consumers value quality more than type 2
– assume z1 > z2 = 0: type 1 consumers only buy if quality is greater
than z1:
• never fly in coach
• never shop in Wal-Mart
• only eat in “good” restaurants
– type 2 consumers will buy any quality so long as consumer
surplus is nonnegative
Chapter 7: Product Variety and
Quality under Monopoly
38
Vertical differentiation 2
• Firm cannot distinguish consumer types
• Must implement a strategy that causes consumers to selfselect
– persuade type 1 consumers to buy a high quality product z1 at a
high price
– and type 2 consumers to buy a low quality product z2 at a lower
price, which equals their maximum willingness to pay
• Firm can produce any product in the range
z, z
• MC = 0 for either quality type
Chapter 7: Product Variety and
Quality under Monopoly
39
Vertical differentiation 3
Suppose that the firm offers two products with qualities z1 > z2
For type 2 consumers charge maximum willingness to pay for the
low quality product: p2 = 2z2 Type 1 consumers
prefer the high quality
Now consider type 1Type
consumers:
firm have
faces an incentive
1 consumers
to the low
quality good
compatibility constraint
nonnegative consumer
high
1(z1 – z1) – p1 >surplus
1(z2 – from
z1) – pthe
2
quality good
1(z1 – z1) – p1 > 0
These imply that p1 < 1z1 – (1 2)z2
There is an upper limit on the price that can be charged for
the high quality good
Chapter 7: Product Variety and
Quality under Monopoly
40
Vertical differentiation 4
• Take the equation p1 = 1z1 – (1 – 2)z2
–
–
–
–
this is increasing in quality valuations
increasing in the difference between z1 and z2
quality can be prices highly when it is valued highly
firm has an incentive to differentiate the two products’
qualities to soften competition between them
• monopolist is competing with itself
• What about quality choice?
– prices p1 = 1z1 – (1 – 2)z2; p2 = 2z2
• check the incentive compatibility constraints
– suppose that there are N1 type 1 and N2 type 2 consumers
Chapter 7: Product Variety and
Quality under Monopoly
41
Vertical differentiation 5
Profit is
P = N1p1 + N2p2 = N11z1 – (N11 – (N1 + N2)2)z2
This is increasing in z1 so set z1 as high as possible: z1 = z
For z2 the decision is more complex
(N11 – (N1 + N2)2) may be positive or negative
Chapter 7: Product Variety and
Quality under Monopoly
42
Vertical differentiation 6
Case 1: Suppose that (N11 – (N1 + N2)2) is positive
Then z2 should be set “low” but this is subject to a constraint
Recall that p1 = 1z1 – (1 - 2)z2 So reducing z2 increases p1
But we also require that 1(z1 – z1) – p1 > 0
Putting these together gives:
The equilibrium prices are then:
z2 =
1 z 1
1   2
 2 1 z 1
p2 =
1   2
(
p1 = 1 z  z 1
Chapter 7: Product Variety and
Quality under Monopoly

43
Vertical differentiation 7
• Offer type 1 consumers the highest possible quality and
charge their full willingness to pay
• Offer type 2 consumers as low a quality as is consistent
with incentive compatibility constraints
• Charge type 2 consumers their maximum willingness to
pay for this quality
– maximum differentiation subject to incentive compatibility
constraints
Chapter 7: Product Variety and
Quality under Monopoly
44
Vertical differentiation 8
Case 1: Now suppose that (N11 – (N1 + N2)2) is negative
Then z2 should be set as high as possible
The firm should supply only one product, of the highest possible quality
What does this require?
From the inequality offer only one product if:
Offer only one product:
N1
2
 1
N1  N 2 1
if there are not “many” type 1 consumers
if the difference in willingness to pay for quality is “small”
Should the firm price to sell to both types in this case? YES!
Chapter 7: Product Variety and
Quality under Monopoly
45
Empirical Application: Price Discrimination
and Imperfect Competition
Although we have presented price discrimination and
product design (versioning) issues in the context of a
monopoly, these same tactics also play a role in more
competitive settings of imperfect competition
Imagine a two-store setting again
Assume N customers distributed evenly between the two
stores, each with maximum willingness to pay of V .
No transport cost—Half of the consumers always buys at
nearest store. Other half always buys at cheapest store.
Chapter 7: Product Variety and
Quality under Monopoly
46
Price Discrimination and Imperfect
Competition 2
If both stores operated by a monopolist, set price = V.
Cannot set it higher of there will be no customers.
Setting it lower though gains nothing.
What if stores operated by separate firms?
Imagine P1 = P2 = V. Store 1 serves N/4 pricesensitive customers and N/4 price-insensitive ones.
The same is true for Store 2.
If Store 1 cuts its price  below V.
It loses N/2 from all current customers
It gains N(V - )/4 by stealing all pricesensitive customers from Store 2
Chapter 7: Product Variety and
Quality under Monopoly
47
Price Discrimination and Imperfect
Competition 3
MORAL 1: Both firms have a real incentive to cut price.
This ultimately proves self-defeating
In equilibrium, both still serve N/2 customers but now
do so at a price closer to cost.
This is especially frustrating in light of the “brandloyal” or price-insensitive customers
Cutting their price does not increase their likelihood
of shopping at a particular place. It just loses revenue.
MORAL 2: Unlike the monopolist who sets the same
price to everyone, these firms have an incentive to
discriminate and so continue to charge a high price to
loyal consumers while pricing low to others.
Chapter 7: Product Variety and
Quality under Monopoly
48
Price Discrimination and Imperfect
Competition 4
The intuition then is that price discrimination may be
associated with imperfect competition and become more
prominent as markets get more competitive (but still less
than perfectly competitive).
This idea is tested by Stavins (2001) with airline prices.
Restrictions such as a required Saturday night stay-over
or an advanced purchase serve as screening mechanism
for price-sensitive customers. Hence, restrictions lead to
lower ticket price.
Stavins (2001) idea is that price reduction associated with
flight restrictions will be small in markets that are not
very competitive.
Chapter 7: Product Variety and
Quality under Monopoly
49
Price Discrimination and Imperfect
Competition 6
Stavins (2001) looks at nearly 6,000 tickets covering 12
different city-pair routes in September, 1995.
She finds strong support for the dual hypothesis that:
a) passengers flying on a ticket with restrictions pay less;
b) price reduction shrinks as concentration rises
In highly competitive (low HHI) markets, a Saturday
night restriction leads to a $253 price reduction but only
a $165 reduction in less competitive ones.
In highly competitive (low HHI) markets, an Advance
Purchase restriction leads to a $111 price reduction but
only a $41 reduction in less competitive ones.
Chapter 7: Product Variety and
Quality under Monopoly
50
Price Discrimination and Imperfect
Competition 5
Variable
Saturday
Night Stay
Required
Coefficient
– 0.408
t-Statistic
Coefficient
– 4.05
-----
t-Statistic
-----
Saturday
Night Stay
0.792
3.39
--------RequiredxHHI
Advance Purchase
--------– 0.023
–5.53
Required
Advance Purchase
--------0.098
8.38
RequiredxHHI
NOTE: HHI is the Herfindahl Index. A Saturday Night Stay or an
Advance Purchase lowers the price significantly. But the HHI terms
show that this effect weakens as market concentration increases.
Chapter 7: Product Variety and
Quality under Monopoly
51
Demand and quality A1
Price
Z2
P(Q, Z2)
When quality is Z2
price is
2/2
Howisdoes
WhenZquality
Z1 increased quality
price is affect demand?
Z1/2
MR(Z2)
Z1
P2 = Z2/2
P1 = Z1/2
MR(Z1)
P(Q,Z1)
/2
Q*

Quantity
Chapter 7: Product Variety and
Quality under Monopoly
52
Demand and quality A2
Price
Z2
Z1
P2 = Z2/2
P1 = Z1/2
So an increase is quality from
Z1 to Z
surplus
2 increases
Social
surplus
at quality
Z2
area
minus
the
is by
thisthis
area
minus
quality
increase in
quality costs
costs
An increase in quality from
The increase in total
Z1 to Z2 increases
surplus
revenue
by this
area Zis greater than
Social
surplus
at quality
1
the
increase
in profit.
is this area minus quality
The monopolist produces
costs
too little quality
/2
Q*

Quantity
Chapter 7: Product Variety and
Quality under Monopoly
53
Demand and quality
Derivation of aggregate demand
Order consumers by their reservation prices
Aggregate individual demand horizontally
Price
1 2 3 4 5 6 78
Quantity
Chapter 7: Product Variety and
Quality under Monopoly
54
Location choice 1
d < 1/4
We know that p(d) satisfies the following constraint:
p(d) + t(1/2 - d) = V
This gives: p(d) = V - t/2 + td
 p(d) = V - t/2 + td
Aggregate profit is then: p(d) = (p(d) - c)N
= (V - t/2 + td - c)N
This is increasing in d so if d < 1/4 then d should be increased.
Chapter 7: Product Variety and
Quality under Monopoly
55
Location choice 2
d > 1/4
We now know that p(d) satisfies the following constraint:
p(d) + td = V
This gives: p(d) = V - td
Aggregate profit is then: p(d) = (p(d) - c)N
= (V - td - c)N
This is decreasing in d so if d > 1/4 then d should be decreased.
Chapter 7: Product Variety and
Quality under Monopoly
56