Stickiness of Rental Rates and Developers’Option
Exercise Strategies
Rose Neng Lai &Ko Wang &Jing Yang
Published online: 6 March 2007
#Springer Science + Business Media, LLC 2007
Abstract In this study we incorporate sticky rents into a real options model to
rationalize the widely documented overbuilding puzzle in real estate markets. Given
the assumption that developers’objective function is to maximize total revenue by
selecting an optimal occupancy level, our model provides a better explanation of the
phenomena we observed in the real world than the traditional market-clearance
based real options models. We also show that developers’exercise strategies can be
affected by the size and the type of property markets. In other words, developers’
exercise strategies could differ among markets and under different conditions.
Keywords Sticky rents .Overbuilding .Real options
Introduction
It is well documented that high vacancy rates exist in most types of property
markets. For instance, vacancy rates in the housing rental market and the office
J Real Estate Finan Econ (2007) 34:159–188
DOI 10.1007/s11146-007-9004-3
Submitted to Cambridge—Maastricht 2005 Symposium.
R. N. Lai (*)
Department of Finance and Business Economics, Faculty of Business Administration,
University of Macau, Taipa, Macau, China
e-mail: RoseLai@umac.mo
K Wang
Department of Real Estate, Baruch College (CUNY), New York, NY, USA
e-mail: Ko_Wang@baruch.cuny.edu
K. Wang IJ. Yang
Department of Finance, California State University-Fullerton, Fullerton, CA, USA
K. Wang
e-mail: kwang@fullerton.edu
J. Yang
e-mail: jyang@fullerton.edu
rental market in the United States were exceptionally high in the 1980s and 1990s. In
particular, the former exceeded 10% in 1986 (Belsky & Goodman, 1996) while the
latter reached as high as 18% in 1990 (Grenadier, 1995). The National Association
of Realtors predicts that the vacancy rates will be 14.5–15.5% for offices, 11–11.5%
for industrial spaces, 8–8.5% for retail spaces, and 5.5–6% for multi-family rental
units in year 2005 (Lereah, 2004). A vacancy rate of 40% or higher in the hotel
industry is also very common (see, for example, McAneny, Han, & Gallagher,
2001). All these vacancy levels are too high to be caused merely by costly searching
and matching processes between households and landlords.
While oversupply in property markets has been widely investigated from different
points of view,
1
only a few studies, such as Grenadier (1996), Wang and Zhou
(2000) and Wang and Zhou (2006), offer theoretical justifications for the results they
present. Grenadier studies the timing of real estate developments using a strategic
option exercise approach based on stochastic demand.
2
He provides an interesting
rationale for a commonly observed phenomenon: increasing development in the
“cold”real estate markets. He believes that panic in the market can induce
preemptive competition in developments during a market downturn, and terms this
phenomenon “irrational construction.”Wang and Zhou advance the standard
strategic real options approach by incorporating both stochastic demand and
construction cost, and allowing multiple players with unequal production capacities
under various market structures. Wang and Zhou are the first to relate overbuilding
to rent collusion with a game theoretical approach. Their model demonstrates that
under competition developers will start construction whenever there is an
opportunity, and that sticky rents led by implicit collusion can be optimal for
developers.
3
In other words, under their model framework, excess vacancies could
be an equilibrium solution in real estate markets.
However, it is fair to say that these three models, while interesting, have certain
weaknesses. The models in Grenadier (1996), and Wang and Zhou (2006) are
basically market clearance models. This type of model is not suitable for explaining
the excess vacancy puzzle because it assumes that any excess space will be absorbed
by adjusting rental rates. Consequently, under these two model frameworks, the
occupancy rate of properties should always be at the 100% level. While Wang and
Zhou (2000) do not impose the market clearance condition, their two-stage model
focuses only on the vacancy rates of markets with the assumption that market rental
rates could be sticky. A major weakness of the paper is that the model does not
1
For instance, Fickes (2001), Johnson (1998), and McAneny et al. (2001) argue that, as long as financing
is readily available and zoning or tax systems are in favor of construction, there is always room for hotel
building. Kummerow (1999) suggests that when a developer considers what her/his rivals will decide, her/
his “rational”development decision may lead to oversupply. Mueller (1999) concludes that rental growth
rates of different real estate markets can be predicted from occupancy level cycles. Hendershott (2000)
points out that the Sydney office market developers failed to incorporate mean reversion in property price
movements, and hence created market cycles.
2
In this model framework, construction decisions can be considered as exercising real options (see for
example Titman, 1985; Williams, 1991 and 1993, for pioneering researches on real options).
3
Pagliari and Webb (1996) also suggest rental properties can be operated at a higher rental rate with a
higher vacancy rate. Additionally, Blackley and Follain (1996) link the increasing rental rate to user costs,
which are in turn related to long-run supply elasticity.
160 R.N. Lai et al.
describe developers’behavior in a dynamic setting. Given this, it is difficult to
understand what drives developers’investment decisions at various stages of the
game. In other words, while their result can be used to predict the vacancy level of a
market, the model does not address the detailed conditions affecting the timing of
developments in different markets.
Our paper attempts to build a model that incorporates the sticky rent argument
developed by Wang and Zhou (2000) into the dynamic options exercise model
setting of Grenadier (1996) and Wang and Zhou (2006). To the best of our
knowledge, this model is the first in the literature that has incorporated sticky rents
into a real options framework. We will then demonstrate that, in a sticky rental rate
setting, our model performs better than traditional market clearance based real
options models in terms of interpreting the essence of overbuilding and vacancies.
Our model starts with an assumption that developers will seek a revenue-
maximizing occupancy level and will allow an optimal excess vacancy rate in the
market. This assumption differs from that used by Grenadier (1996) and Wang and
Zhou (2006), for which developers will adjust rent levels to eliminate all excess
supplies. Our model also differs from Grenadier in that we use the expected mean
time to estimate development intensity, as opposed to the expected median time used
by Grenadier. The use of expected mean time allows us to obtain closed form
solutions (as opposed to simulations in Grenadier, 1996) for the timing of
developments and the time lag between developers’construction decisions. With
closed form solution, it is easier to analyze how the various factors might affect a
developer’s supply decision in terms of magnitude and direction.
Our model provides two important implications that differ from the existing
literature. First, we show that an increase in demand variance will decrease the speed
of developments. It should be noted that, with identical stochastic factors in both
models, our result contrasts to the prediction in Grenadier (1996) that an increase in
demand variance will increase development activities.
4
Second, we show that the
impacts of demand elasticity on developers’exercise decisions can be different when
developers adopt different negotiating strategies. When developers collude with each
other to set an optimal rental rate, an increase in demand elasticity will delay overall
development activities. This result contrasts to the model prediction provided by
Wang and Zhou (2006). Under the market clearance framework, they predict that an
increase in demand elasticity will increase overall development activities.
This paper is organized as follows. The next section presents the model
framework. In “Developers’Game with a Market Clearance Condition,”we will
derive a duopolistic market equilibrium where rents are adjusted to clear the market
so that all the excess capacity is eliminated. In “Strategic Exercises with
Overbuilding,”we will deduce the optimal collusive rent that developers should
adopt and the conditions when overbuilding is preferred. We also generalize the
explanation of overbuilding when rigid rates exist. “Market Clearance versus
Overbuilding”compares the overbuilding model with the market clearance model.
Finally, “Conclusion”concludes.
4
However, our result using one stochastic factor conforms to the result derived by Wang and Zhou (2006)
using both demand and construction cost as the stochastic factors in the model.
Stickiness of Rental Rates and Developers' Option Exercise Strategies 161
Model Framework
Our model relies on several well known assumptions in the field. First, we use the
standard assumptions for financial options that investors prefer more to less, the
demand shock process follows a random walk with a known growth rate and variance,
and the risk-free rate is constant and known. Second, we impose a risk neutrality
condition, which basically states that the discount rate is equal to the risk-free rate (see
Cox & Ross, 1976; Harrison & Kreps, 1979; and Merton, 1975, for the discussion of
this assumption). Finally, we assume an incremental demand function that is
inversely related to the rental rate, or
DX tðÞ;RtðÞ½¼aX tðÞbR tðÞ ð1Þ
where aand bare constants, X(t) is the multiplicative demand shock at time t, which
may represent changes in the number of households or in the standard of living due
to changes in market conditions, consumers’taste, and other factors affecting
demand. R(t) is the rental rate at time t.
The multiplicative demand shock X(t)inEq.1follows a geometric Brownian motion
5
dX ¼mXdt þsXdw;ð2Þ
where wis a random variable following a Wiener process, that is, with a normal
distribution with E(dw)=0, and Var(dw)=dt.μis the constant instantaneous growth rate
of the demand shock per unit time, and σis the constant instantaneous standard
deviation per unit time with respect to w. Equation 2states that the instantaneous change
in demand shocks governing the rental rates is its rate of return plus the standard deviation
times the instantaneous change in the Wiener process governing its randomness.
Next, consider a simple duopoly market in which each of the two developers own
a parcel of land for construction.
6
Both are said to own construction options that can
be exercised whenever they see a fit. Unlike financial options that generate perpetual
dividend yields immediately after exercise, there may be a few years of construction
before rental income can be realized. Hence, we assume it takes δyears to complete
the construction. A developer who decides today to build the rental unit at time t
will receive rental income only after time t+δ. We assume that the two developers
will exercise their developments in sequence. We term the first developer as the
Leader and the second developer as the Follower. Both developers will be indifferent
to being the Leader or the Follower if the equilibrium payoff (to be solved by the
model) of the Leader is the same as that of the Follower.
5
Other types of shocks can certainly be accommodated. For instance, Wang and Zhou (2006) work on
two stochastic processes, one describing demand and another describing the construction costs. Riddiough
(1997) incorporates the probability of regulatory changes into the land option value. Martzoukos and
Trigeorgis (2002), on the other hand, work on mixed jump-diffusion process to describe the impact of rare
events on the value of the underlying assets. However, most real option models use a geometric Brownian
motion to describe the shock probably because it is easier to derive a closed-form solution using this
particular process.
6
A duopoly, the simplest form of oligopoly, is assumed for the purpose of simplicity. Wang and Zhou
(2006) relax this assumption to an oligopoly and a competitive market, finding that the results are very
similar to a duopoly case.
162 R.N. Lai et al.
The value of the building option for each unit that a developer supplies at the time
of decision-making is equal to the discounted perpetual rent series received after the
rental unit is built (analogous to a constant-growth dividend discount model), that is
Vt;XðÞ¼sup
t
Et;XðÞerterμðÞδRX tþδðÞ½
rμðÞ
I
;ð3Þ
where ris the risk-free rate, and tis the date when construction commences. The
first term within the inner parentheses in Eq. 3represents the perpetual rent flow
discounted to time t; while the second term represents any costs incurred during
construction and assumed paid in one lump sum at time t. (Note that r−μis the
capitalization rate for a constant growth income stream.)
Applying Ito’s Lemma, the option value before exercising possesses an
instantaneous rate of change of
dV ¼1
2s2X2@2V
@X2þmX@V
@Xþ@V
@t
dt þsX@V
@Xdw:ð4Þ
If the time of valuation is assumed as today (t=0), the payoff function will be
invariant with time, and becomes
VXðÞ¼sup
t
EXðÞerμðÞδRX tðÞ½
rμðÞ
I
:ð5Þ
As there is no interim payoff from the bare land before construction, the expected
rate of return from holding the development option should be equal to the risk-free
rate according to the risk neutrality argument. Hence, equating the expectation on
Eq. 4to the risk-free rate (we assume a flat yield curve for simplicity),
7
we obtain an
equation governing the rental flow as
1
2s2X2d2V
dX 2þmXdV
dX rV ¼0:ð6Þ
In the following section, we will deduce the optimal construction conditions in a
sub-game Nash equilibrium, where the rental rate considered is the ordinary market
equilibrium rate that clears the market. Sticky rates will be imposed later in
“Strategic Exercises with Overbuilding.”
Developers’Game with a Market Clearance Condition
Development Strategies
When a developer begins construction, she/he will pay the construction cost and
receive rent flow when the building is completed. At equilibrium with market
clearance, the rent will always be adjusted until all units are occupied. This means
that all the existing space, denoted as M, is already fully occupied. Therefore, the
7
Brennan and Schwartz (1980) and Kim, Ramaswamy, and Sundaresan (1993) have shown that constant
interest rate models yield negligible calculation errors. Given this, it is common to assume a flat yield
curve when using a real option model.
Stickiness of Rental Rates and Developers' Option Exercise Strategies 163
incremental demand level in Eq. 1will be equal to the number of newly developed
properties, Q(t), and hence the rental rate determined by demand takes the form
RX tðÞ½¼cX tðÞ1
bQtðÞ;ð7Þ
where c¼a
b. The parameter, b, provides a measure of price elasticity.
Specifically, when the market has only the Leader’s supply Q
L
, the Leader can
enjoy a rental rate of
RX tðÞ½¼cX tðÞ1
bQL:ð8Þ
When the Follower decides to enter the market by building Q
F
units of rental space,
the increased supply will drive down the rental rate to
RX tðÞ½¼cX tðÞ1
bQ;ð9Þ
where Q¼QLþQF
8
. The Follower will experience only one demand function 9,
while the Leader will have both demand functions, first Eq. 8and subsequently Eq. 9.
Thus, the Leader’s strategy embeds that of the Follower. This chain of interactive
decisions constitutes a game between the two developers in equilibrium.
With standard backward induction, we first solve for the Follower’s market
equilibrium construction strategy and then work backward to determine that of the
Leader. We redefine the payoff V(X) in Eq. 5as F(X) for the Follower, and L(X) for
the Leader.
To solve Eq. 5for the Follower, F(X) must satisfy the following boundary
conditions (see Dixit & Pindyck, 1994, for more discussions)
F0ðÞ¼0;ð10aÞ
FX
e
F
¼ermðÞdcX e
F1
bQ
rmðÞ
I;ð10bÞ
F0Xe
F
¼ermðÞdc
rmðÞ
;ð10cÞ
where Xe
F, the ‘trigger point,’is the level of demand shock with which the Follower
should start construction (the superscript eis used to denote the demand trigger
under market clearance; owill be used in the case of overbuilding in the next
section). The first boundary condition is the absorbing barrier specifying that the
development option will remain zero forever once the rental rate hits zero. The value-
matching condition (10b) simply states the payoff at the time of exercising the option.
The last is the smooth-pasting condition that ensures an optimal value for F(X)atXe
F
(also known as the ‘high-contact’condition by Merton, 1973).
8
Q
L
and Q
F
do not need to be identical. For example, Wang and Zhou (2006) allow for developers with
uneven production capacity.
164 R.N. Lai et al.
Proposition 1 In equilibrium with a market clearance condition, the optimal
demand shocks that trigger developments are
Xe
L¼1
c
1
bQLþermðÞdrmðÞI
;ð11Þ
Xe
F¼b
cb1ðÞ
1
bQþermðÞdrmðÞI
;ð12Þ
where b¼1
2m
s2þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
m
s21
2
2þ2r
s2
q, and Xe
L<Xe
F.
Proof See Appendix.▪
Proposition 1 indicates that, in equilibrium with a market clearance condition,
when the demand shock is lower than Xe
L, no developer will invest. When the
demand shock reaches Xe
L, one will develop at once (and become the Leader), while
the other will wait until Xe
Fis reached (and become the Follower). Notice that since
the equilibrium payoffs will be the same for the Leader and the Follower, both
developers are indifferent between these two positions. (In other words, one
developer can be a Leader by chance, while the other will be the Follower.) Should
the demand shock reach Xe
Fbefore any construction occurs, both developers will
start building simultaneously and become joint developers. (The minimal time lag
between the developments, if any, can be neglected). In other words, different
market equilibria can be attained when the incremental demand shock reaches
different thresholds.
Causes for Asymmetric Development Strategies
It is easy to see that both trigger points in Eqs. 11 and 12 are positively affected by
new supply levels (Q
L
and Q, respectively), and the associated construction costs I.
The interpretation is simple. Developers need to wait for higher demand shocks that
can clear a market when there is a bigger supply, and/or that can generate acceptable
revenue to break even when the construction is more costly (any shock beyond the
trigger point level will bring her/him positive net income).
The optimal demand shocks in Eqs. 11 and 12 show that the Follower’s strategy
to begin construction (when the demand shock Xe
Fis realized) differs from that of the
Leader both in the level of new supply (that is, Qversus Q
L
) and in the term b
b1ðÞ
.In
fact, by rewriting Eq. 11 into Xe
L¼QL
bc þeðrmÞdrmðÞI
c, we can interpret the first
component as the demand shock that clears new supply, and the second component
as the demand shock that makes the developer break even (which can be called the
“reservation shock”). We can also rewrite Eq. 12 into two components in a similar
way.
Since the term b
b1ðÞ
>1, the Follower will wait longer than the Leader before
starting the development. When the Follower chooses the exercise time, the Leader
Stickiness of Rental Rates and Developers' Option Exercise Strategies 165
is already in the market. As such, the Follower does not need to worry about the
possible preemption of the rival. Hence, the Follower’s decision is simply a standard
option pricing problem that maximizes her/his own option value, and is affected by b
in a similar way as other real options. Transforming Eq. 12 into Xe
F¼1
c11
β
ðÞ
1
bQþerμðÞδrμðÞI
, we see that bnegatively affects Xe
F. In other words, a high
b, by affecting the development option value, leads to an early exercise.
In contrast, when the Leader chooses the exercise time, she/he has to consider the
Follower’s optimal exercise strategy. As shown in the Appendix,Xe
Lis solved by
making the Leader indifferent between being a Leader and being a Follower, rather
than by maximizing her/his own option value. Correspondingly, the Leader’sdecision
is based on the relative values of the Leader and the Follower at the moment the
Leader begins construction. With the option value that takes the functional form
LXðÞ¼BX bfor the Leader (versus FXðÞ¼AX bfor the Follower),
9
the relative
values depend on Aand B, but not the exponent b. The difference in these option
values stems from the construction sequence asymmetry of the two developers, which
contributes to their behavioral disparities in some aspects of the real estate market, as
we will show in Corollary 1 below (and later on in Corollary 2 when the market
clearance condition is absent).
Impact of External Conditions on Strategies with Market Clearance
In this subsection, we first estimate when the development triggering shocks will arrive
so that the developers will start their developments, and then analyze the impacts of
exogenous factors on the development timing of each developer and their development
time lag.
With Dynkin’s Equation (see Øksendal, 1998), the expected times when the
Leader and the Follower start constructing the rental units from a current date t
0
are
Et
e
L
¼ln Xe
L
ln X t 0
ðÞðÞ
μ1
2σ2and Et
e
F
¼ln Xe
F
ln X t 0
ðÞðÞ
μ1
2σ2;ð13Þ
respectively. Correspondingly, the expected time lag between the two developments is
Ete
LF
¼In Xe
F
ln Xe
L
μ1
2σ2:ð14Þ
The comparative static analyses on Et
e
L
,Et
e
F
and Ete
LF
are reported in Corollary 1.
Corollary 1 In equilibrium with a market clearance condition, the time to start
construction is increasing in market uncertainty, while decreasing in demand
elasticity for both developers. That is,
@Et
e
L
@σ>0;@Et
e
L
@b<0;@Et
e
F
@σ>0;and @Et
e
F
@b<0:
9
As shown in the Appendix, the exponents in both developers’option value functions, βs, are the same.
166 R.N. Lai et al.
However, the magnitudes of the effects differ across developers, and the time lag
between their developments is increasing in market uncertainty, while decreasing in
demand elasticity. That is,
@Ete
LF
@s>0;and @Ete
LF
@b<0:
Proof See Appendix.▪
Corollary 1 indicates that the Leader and the Follower react consistently to the
changes of market uncertainty σand demand elasticity b, but to different extents due
to their asymmetric positions in the sequence of construction.
It is well known that uncertainty increases the real option values. Similarly, our
results, @Et
e
L
ðÞ
@σ>0, @Et
e
F
ðÞ
@σ>0, and @Ete
LF
ðÞ
@σ>0, suggest that the development options are
more valuable with higher demand uncertainty. Developers will be more cautious
and willing to wait longer to start their developments. The mean exercise time lag
between the Leader and the Follower will also be longer.
Contradicting our analytical results, Grenadier’s(1996) numerical result shows
that the median exercise time lag between the Leader and the Follower should be
shorter when demand is more volatile. Grenadier’s result is surprising and counter-
intuitive because it suggests that developers will accelerate their development
activities when they are less certain about the future demand. Although it is possible
that the difference between Grenadier’s and our results could be due to the fact that we
use different parametric values, we believe that such a difference could be attributed to
the use of mean time (our model) versus median time (Grenadier’s model).
10
It should be noted that the movement of geometric Brownian motion is based on
percentage change. When applying this motion to a developer’s exercise strategy,
there will be two opposite forces. On one hand, high demand volatility increases the
probability that the demand level will hit the trigger point in the short run. In this
regard, higher demand volatility might shorten a developer’s exercise time. On the
other hand, in the long run, the demand level should reach zero when demand
volatility is sufficiently large (see Øksendal, 1998, for a formal proof of this
proposition). Intuitively, consider a case in which the demand level starts at 100
units. The demand level will go up 10% and move down 10% (in a random order) in
the next two periods. It is easy to see that the demand level will be lower than 100
units at the end of the second period. The demand level will be even lower when the
percentage change (the volatility) is larger than 10%. (If the variance is sufficiently
large and the growth rate is zero, the demand level might approach zero at a certain
point, and there will be no exercise in the future.) This indicates that it will be more
10
To the best of our knowledge, most papers that analyze option-exercise time issues use the mean.
Grenadier (1996) justifies the use of the median by pointing out that the average time is undefined when
μ<1
2σ2.However, in order to make the expectation infinite, the demand volatility must be extremely
large. When μ=0.02 (a parameter used in Grenadier’s simulation analysis), σmust be greater than 0.20 in
order for μ<1
2σ2.In other words, the standard deviation of the percentage change in demand must be
more than ten times the expected percentage change in demand to make the average time infinite. In most
situations, we should not need to worry about this possibility.
Stickiness of Rental Rates and Developers' Option Exercise Strategies 167
difficult for the demand level to hit the trigger point in the long run if it cannot be
reached in a short period.
Given these two opposite forces, it is clear that the use of mean and median could
result in opposite conclusions. Since the use of median neglects the long tail on the
right side of the distribution (the longer expected time), it is possible that high
demand volatility might decrease the median exercise time between the two
developers. However, because our model prediction is based on analytical results
while Grenadier’s result is based on simulations, we believe that our analysis based
on the mean exercise time should offer a more complete picture than that based on
the median exercise time.
Note that market volatility exerts a more significantly negative effect on the
Follower’s development than on the Leader’s, as indicated by @Ete
LF
ðÞ
@σ>0. This is also
attributed to the asymmetry in the sequence of development. From Eqs. 11 and 12,
we can see that the parameter, b, which is negatively affected by volatility, appears
in the trigger point solution for the Follower but not for the Leader. A higher
volatility increases the value of exercise option while it decreases the value of
development (reflected by a lower bvalue), causing the Follower to further delay
her/his development and lengthen the time lag from the Leader.
In terms of demand elasticity b, the time of development is negatively affected, as
confirmed by our results that @Et
e
L
ðÞ
@b<0 and @Et
e
F
ðÞ
@b<0. With the market clearance
condition, the market rent has to drop to clear the market if there is an increase in
supply. A lower elasticity means that the rent has to drop relatively more than in case
of higher elasticity in order to clear the market. Therefore, developers will delay the
development exercise when demand elasticity is low. Note that waiting becomes
valuable if the market demand is extremely inelastic (or bis very small). Such effect
is more pronounced in the case of the Follower, which is why the time lag of the two
developments will be widened, as suggested by @Ete
LF
ðÞ
@b<0. The intuition can be seen
from Eqs. A.7 and A.11 in the Appendix.@Xe
L
@b¼QL
b2cand @Xe
F
@b¼ bQ
b1ðÞb2cimply that
the Follower needs to clear more new supply than the Leader (Q¼QLþQFversus
Q
L
). They also imply that the Follower needs to wait for a larger demand increase
(by a factor of b
ðb1Þ) than the Leader before exercising the development option. Both
factors magnify the development time gap between the Leader and the Follower.
Strategic Exercises with Overbuilding
The previous section presents the optimal development strategies under market
equilibrium in which the rental rates are always adjusted so that demand equals
supply. In reality, developers are often reluctant to reduce the rental rate to eliminate
all supply. This is rational if the total rental income can be maximized, albeit with
some vacancy. In this section, we develop a strategic game where oversupply occurs
when developers collude on a sticky rent, and provide explanations on why a
collusion outcome is optimal. As in Wang and Zhou (2000), there are two stages in
the game: the developers choose their optimal time to construct in the first stage, and
choose the optimal collusive rent in the second stage. With backward induction, we
solve for the collusive rent first, and then the optimal times for construction.
168 R.N. Lai et al.
Collusion in Rent
In this section, our model starts with two assumptions for the property rental market.
First, we assume that landlords are able to adjust the rental rate of properties in short
intervals. (This could be an accurate description for commercial properties that have
hundreds of tenants with different maturities.) In addition, we assume that the rent
information can be observed by market players in a short interval. (This assumption
is particularly true for large metropolitan areas where several information gathering
and rental agents are active in the market.) With these two assumptions, the
determination of rental rates in a given market can be viewed as an infinitely
repeated game with perfect information among players (landlords).
Under this framework, the well-known Folk Theorem indicates that the collusion
(or Pareto) outcome (rent level) will dominate the Nash equilibrium as long as all the
players are patient (see, for example, Abreu, Dutta & Smith, 1994, and Aumann,
1959,1960,1981). The intuition behind this theorem is simple. When players can
retaliate at their opponents’current predatory actions in their long-term interactions,
predatory behaviors will not be optimal. Related to this, Friedman (1971) shows that
a Pareto outcome can be supported in a perfect equilibrium of a repeated game if any
player’s deviation from Pareto will induce other players to revert to Nash
equilibrium for the remainder of the game.
Although games in the real world may not be repeated infinitely due to limited
life spans of the players, Fudenberg and Maskin (1986) point out that, from
anecdotal and experimental evidence, a cooperative strategy is a likely outcome as
long as there are a large (even though finite) number of repetitions. Numerous
studies also point out that a collusion is still the favorable outcome even if (1) the
information on the number of repetitions is slightly imperfect to players (see
Neyman, 1999), (2) when players have some “irrationality”because of incomplete
information about players’options or motivations (see Fudenberg & Maskin, 1986
and Kreps, Milgrom, Roberts & Wilson, 1982), or (3) when a slight departure from
the strict Nash equilibria is acceptable by a player who is not perfectly rational
(Radner, 1980). To sum up, the literature on the repeated games seems to indicate
that cooperation is the optimal outcome as long as players’actions can be observed
by other players in the market and players in the market can retaliate promptly if
other players deviate from the agreed strategies. It is fair to say that most property
rental markets we observe exhibit the two characteristics that will ensure a
cooperative game.
Wang and Zhou (2000) apply the Folk Theorem to study the sticky rental rate and
the overbuilding phenomenon. They use a two-stage game framework to prove that
it is optimal for developers to collude on rents as long as they are allowed to adjust
rental rates reasonably promptly (consistent with the framework of an infinite
repeated game) and if the discount rate used by the developers is not substantial (that
is, the present value of future penalties associated with the low perpetual Bertrand
payoff is significant, consistent with the “patience”presumption of the Folk
Theorem).
11
11
See Proposition 1 of Wang and Zhou (2000) for the formal proof of (and detailed conditions for) an
optimal sticky rental rate.
Stickiness of Rental Rates and Developers' Option Exercise Strategies 169
The intuition for this phenomenon is very simple. Once a collusive rent is set, one
developer will try to deviate from the collusive rent only if the developer can benefit
from this “cheating”strategy. However, every developer realizes that, if one
developer lowers the rent, all other developers will follow the strategy; and when all
other developers follow the strategy, the rent will drop to the level that the
occupancy rate for all properties in the market reaches to 100%. Since the rental rate
at the full occupancy is below that under the collusion, every developer will suffer.
This means that all developers will receive a lower rent (than the collusive rent) from
the moment on and into perpetuity.
Given this, before any developer decides to cheat, she/he has to compare her/his
one time gain by cheating (by reducing the rental rate, where a developer can
exhaust her/his supply and earn a one time better payoff than all other developers in
the market during a short period) with the potential loss when all other developers
retaliate (where all developers will earn a perpetual income that is much lower than
collusive income thereafter). When rents can be adjusted very conveniently, the
temporarily high profit that a developer earns from cheating will quickly evaporate,
while the present value of penalties (lower rents) will be overwhelming when
compared with the benefit of cheating. Given this, Wang and Zhou (2000) argue that
there is no incentive for a developer to cheat by deviating from the collusive rent and
it is possible for a property rental market to exhibit a sticky rental rate.
Since the conditions specified (and arguments advocated) for a sticky rental rate
by Wang and Zhou (2000) seem to conform to at least some commercial markets we
can observe in the real world, our model in the section starts with the assumption
that there is an optimal rent level (and hence, an optimal occupancy rate) in the
market. To accommodate this assumption, we define an effective rental rate as the
product of the sticky rental rate and occupancy level (which is now less than unity), or
Effective Rental Rate ¼Occupancy Rental Rate per Unit of Rented Space:
Given this definition, we can replace the incremental demand function in Eq. 1with
e
D¼aX tðÞbRt;ð15Þ
where Rtis the sticky rental rate selected by the landlord/developer for each unit of
rental space at time t. This sticky rental rate is achieved to maximize the developers’
collusive revenue, rather than to clear the market.
With the absence of the market clearance condition, the existing space Mhas a
vacancy rate v. Correspondingly, the total market demand equals 1 vðÞMþe
D, and
we have a total occupancy rate of k¼1vðÞMþ~
D
MþQtðÞ (0≤k≤1). The pro rata effective
rental rate for each rental unit (vacant and occupied) at time tis therefore
RX tðÞ½¼kRt¼1vðÞMþaX tðÞbRt
MþQtðÞ Rt:ð16Þ
Given this, the total revenue for all developers in the market equals total units
supplied multiplied by the effective rental rate, that is
TR Rt
¼kMþQtðÞðÞ
Rt¼1vðÞMþaX tðÞbRt
Rt:ð17Þ
170 R.N. Lai et al.
It should be noted that, for simplicity, we do not explicitly distinguish between
the natural vacancy rate and the excess vacancy rate when discussing the vacancy
rate. However, the existence of the natural vacancy can be easily incorporated into
our model. We can follow Jud and Frew’s(1990) work and define the natural
vacancy rate as a level where landlords will not willingly adjust rents anymore.
12
With this definition and by assuming demand elasticity is infinite when the vacancy
rate reaches the natural vacancy level,
13
the effect of the natural vacancy rate can be
reflected in Eq. 17. Since developers will select the optimal rent (and hence the
optimal occupancy level) based on Eq. 17, the assumption that demand elasticity is
infinite when the vacancy rate reaches the natural vacancy level ensures that the
impact of natural vacancy rate on investment decision is implicitly considered in the
optimization process.
Following Wang and Zhou (2000), our model setup implies that the developers of
new units compete with existing vacant units for market demand.
14
At any given
level of demand shock, X(t), the optimal rigid rental rate, R*, that developers will
stick to is one that maximizes the total revenue function (17). That is
R*¼1
2b1vðÞMþaX tðÞ½:ð18Þ
Correspondingly, the optimal occupancy rate is
k*¼1vðÞMþaX tðÞ
2MþQtðÞ½
;ð19Þ
and the optimal effective rental rate in Eq. 16 becomes
R*XtðÞ½¼
1vðÞMþaX tðÞ
2
4bMþQtðÞ½:
2
4ð20Þ
When the Leader enters the market by supplying Q
L
, all developers should
optimally rent at RL*.
15
Then, when the Follower enters the market, the new rental
rate should be adjusted. The issue is what level of demand shock can actually
optimize all developers’total revenue and sustain equilibrium (that is, when the
strategic game holds). Certainly, the demand shock trigger points Xe
Land Xe
Ffound
in “Developers’Game with a Market Clearance Condition”in which the resulting
12
One of the causes of natural vacancy is the matching delay between supply and demand, as mentioned
in Read (1988).
13
At this flat end of the demand function, renting out any additional unit cannot increase the total rental
income any further because the costs of providing more services by landlords, such as searching and
leasing costs as well as loss of tenants, become very high. In fact, Gabriel and Nothaft (1988) posit that
landlords may strategically hold some vacant units for the purpose of maximizing net rental income, given
imperfect information and rigid lease agreements.
14
It should be noted that any demand function can be applied in place of the revenue equation as long as
the total revenue function thus generated is concave, and hence ensures a unique maximum.
15
We continue to follow the notion of Leader and Follower as in “Developers’Game with a Market
Clearance Condition.”
Stickiness of Rental Rates and Developers' Option Exercise Strategies 171
optimal rental rates and occupancy rates have not been considered are no longer
applicable. The new triggers are derived in the following subsection.
Overbuilding
Following the approach adopted in “Developers’Game with a Market Clearance
Condition,”we will deduce the optimal demand shocks for the Follower and the
Leader, Xo
Fand Xo
L, respectively, given the rigid rent in Eq. 18. These will lead to
market situations with the coexistence of an (optimal) vacancy rate, 1 –k*, and total
maximized revenues for all developers (whose supplies include previously vacant
space as well as new supplies).
Proposition 2 In the strategic game with overbuilding, the optimal demand shocks
that trigger developments are
Xo
L¼1
affiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4ermðÞdIrmðÞbMþQL
ðÞ
q1vðÞM
;ð21Þ
Xo
F¼1
ab2ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4bb2ðÞerμðÞδIrμðÞbMþQðÞþM21vðÞ
2
qb1ðÞ1vðÞM
:
ð22Þ
where b¼1
2m
s2þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
m
s21
2
2þ2r
s2
q,and Xo
L<Xo
F.
Proof See Appendix.▪
From Eqs. 21 and 22, it is easy to see that the two factors affecting Eqs. 11 and 12
still persist. First, the trigger points are positively affected by the new supply levels,
Q
L
and Q, respectively. With more new supply, the developers will have incentives
to wait for a larger demand shock before exercising their options in order to repress
the vacancy rate. Second, the trigger points are positively affected by the investment
costs. The developers still need to wait for a larger demand shock to generate
acceptable revenue when the buildings are more costly to construct. Moreover,
similar to the market clearance situation, the construction sequence asymmetry still
exists. The trigger shock functions for the Leader and the Follower differ in both the
levels of new development supply (Qas versus Q
L
) and the functions of b.
A major difference between this model and the market-clearance model is that,
with rent collusion, the trigger points decrease with more existing demand, measured
by (1−v)M. Given a higher existing demand, from R*¼1
2b1vðÞMþaX tðÞ½in
Eq. 18, we know that the equilibrium collusion rents should be higher for any
demand shock, hence motivating earlier developments. A similar rationale also
applies to Eq. 22. However, despite the complexity of the trigger value formula in
Eq. 22 relative to Eq. 21, it is easy to see that both positive and negative effects from
existing demand coexist on Xo
F, making (1−v)Mless negatively associated with Xo
F
than with Xo
L.
172 R.N. Lai et al.
Impact of External Conditions on Strategies with Overbuilding
In this subsection, we analyze the impacts of exogenous factors on the degree of
stickiness in the rental rates, and therefore the persistence of overbuilding. On this,
however, we will focus on two parameters: the demand elasticity band the existing
supply M, because the implications of the market uncertainty σare similar to those
reported in Corollary 1.
16
The demand elasticity is now of greater importance
because of its close relation with the rent stickiness. In addition, given the strategic
game with collusion, the existing supply which does not play a role in the strategic
game with market clearance, will become a crucial factor in the formation of rental
rates, the extent of overbuilding, and hence, the timing of developments. Our
analytical results derived using Proposition 2 is reported in Corollary 2.
Corollary 2 In the strategic game with overbuilding, the time for the Leader to start
her/his construction is increasing in demand elasticity and decreasing in existing
supply; and the corresponding sticky rent is decreasing in demand elasticity and
increasing in existing supply. That is,
@Et
o
L
@b>0;@Et
o
L
@M<0;@Ro
L
@b<0 and @Ro
L
@M>0
In contrast, the time for the Follower to start her/his construction is increasing in
demand elasticity and decreasing in existing supply; and the corresponding sticky
rent is decreasing in both demand elasticity and existing supply. That is,
@Et
o
F
@b>0;@Et
o
F
@M<0;@Ro
F
@b<0 and @Ro
F
@M<0
In addition, the time lag between their developments is decreasing in both demand
elasticity and existing supply. That is,
@Eto
LF
@b<0 and @Eto
LF
@M<0:
Proof See Appendix.▪
In terms of demand elasticity b, the insight from Corollary 2 is interesting and
rich. First, contradicting the results derived in “Developers’Game with a Market
Clearance Condition,”we find that @Et
o
L
ðÞ
@b>0 and @Et
o
F
ðÞ
@b>0. In other words, if
developers are allowed to collude on rents, they will accelerate their exercises
whenever demand elasticity is low. The intuition is simple. From Eq. 20, we see that
@R*
@b<0 for any demand shock. That is, a lower demand elasticity will increase the
effective rental rate and hence the development revenue. This is confirmed by @Ro
L
@b<
0 and @Ro
F
@b<0. In other words, a lower demand elasticity makes developments more
attractive, leading to earlier exercises of development options. Therefore, as opposed
16
See the Appendix for our proof on the derivatives of the developers’expected times to start construction
and their construction time lag with respect to market volatility, σ.
Stickiness of Rental Rates and Developers' Option Exercise Strategies 173
to the market clearance condition in “Developers’Game with a Market Clearance
Condition”where market rent has to drop to clear excess supply, when rent collusion
is possible, developers can adjust rent (and correspondingly the vacancy rate) to a
level that optimizes total revenue.
It should also be noted that the demand elasticity exerts different degrees of
influence on the two developers. The result, @Eto
LF
ðÞ
@b<0, indicates that when demand
becomes less elastic, the Leader will speed up construction at a faster pace than the
Follower. As a consequence, the time lag of the two developments will be enlarged.
The mathematical interpretation of this result is as follows. Comparing @Xo
L
@band @Xo
F
@bin
Eqs. A.20 and A.26 in the Appendix, we see that the existing demand (1 −v)Mis
embedded within the effect of demand elasticity on the Follower’s trigger point. As
discussed earlier, the existing demand has a positive effect on Xo
Fbut not on Xo
L.Asa
result, the sensitivity of the Follower’s trigger point to demand elasticity is reduced,
leading to @Xo
F
@b<@Xo
L
@b, and hence @Eto
LF
ðÞ
@b<0.
Our result can help us understand better the market structure for different types of
property markets. In property markets with high demand elasticity (such as office
and retail), the construction decisions should not differ much whether developers
collude or not. In other words, if we assume that owners of class A office buildings
and super-regional malls find it easier to collude on rents than the owners of class C
office buildings and neighborhood malls, we would expect that the overall vacancy
rates between the high quality and low quality properties in these two types of
markets would not differ much.
On the other hand, the story could be different for property markets with a low
demand elasticity (such as hotel and storage). Given this, if we assume that
developers can collude on rents for better constructed hotels and storage facilities,
but not for mediocre hotels and storage facilities, holding everything else constant,
we would expect to see more developments on the high end of these two property
markets than the low end of the markets. We suggest that an empirical validation on
this proposition is warranted.
In terms of existing supply M, the results also generate important implications.
First, the derivations of @Ro
L
@Mand @Ro
F
@Min Eqs. A.23 and A.29 in the Appendix show that
the rents can be affected by Min two opposite ways. On one hand, holding the
existing vacancy rate constant, a bigger Mcorresponds to a bigger existing demand,
thus leading to a higher rent. On the other hand, a bigger Minduces earlier exercises,
hence reduces the equilibrium demand shock triggers, and leads to lower rents. The
result @Ro
L
@M>0 indicates that the former effect dominates the latter for the Leader, while
@Ro
F
@M<0 indicates the latter effect dominates the former for the Follower.
Moreover, we have @Et
o
L
ðÞ
@M<0 and @Et
o
L
ðÞ
@M<0. When there are already many existing
units in the market, there is an incentive for developers to increase the speed of
development. A possible explanation is that the total vacancy rate in the market (as a
weighted average of the vacancy rate of the existing space and the vacancy rate of
the new space) will be less sensitive to the vacancy rate of the new space if there is a
large amount of existing supply. (Under this circumstance, the weight of the new
supply will be smaller when compared with the weight of the existing supply). In
other words, developers have more incentives to build as long as the consequence of
the overbuilding can be shared by many other developers in the market. This finding
might shed light on the persistent excess vacancies in property markets, a puzzle in
174 R.N. Lai et al.
real estate research for decades. Our prediction is also consistent with the prediction
from Wang and Zhou (2000)’s static model in that developers might be able increase
their profits by offering more supplies if the existing supplies are large enough.
The result that @Eto
LF
ðÞ
@M<0 indicates that the effect of existing supply on new
development is stronger for the Follower than for the Leader. That is, the Follower
will speed up development more actively than the Leader. This result is intuitively
simple. Since new supplies share the market with existing capacity, after entering the
market, the Leader’s new supply becomes existing inventory when the Follower
makes a decision. With a larger existing inventory, it is not surprising to see that the
speed of exercise is faster for the Follower than for the Leader.
The implication of this finding on real estate markets is interesting. Holding other
things constant, it implies that developers will have more incentives to build when
the market size is large, but not if the market size is small. If this implication is
correct, we should observe that large markets would constantly exhibit a high level
of excess vacancy. This should be valid because developers will have the incentives
to capture all the development opportunities if others will share the consequence
with them when things go bad. On the other hand, developers in a market with small
inventory will be more careful in their construction decisions because they will have
to bear the consequences on their own. Given this, we should observe that in large
markets, the vacancy rates will be consistently higher than their natural vacancy
rates. In the contrast, for a small market, there is a chance that the vacancy rate will
be low or around its natural vacancy rate. This is a proposition that can be
empirically tested.
Market Clearance versus Overbuilding
In this section, we compare the construction strategies under the market clearance
condition to that in a market with sticky rents. Intuitively, we expect developments
to begin earlier if there are sticky rents, which is confirmed by the following
corollary.
Corollary 3 In equilibrium, a development under a sticky rental rate condition
starts earlier than under a market clearance condition, as shown by
Et
o
L
<Et
e
L
and Et
o
F
<Et
e
F
;
and the time disparity is enlarged with an already abundant existing supply or a low
demand elasticity, as shown by
@Et
e
L
Et
o
L
@M>0;@Et
e
F
Et
o
F
@M>0;@Et
e
L
Et
o
L
@b<0 and
@Et
e
F
Et
o
F
@b<0:
Stickiness of Rental Rates and Developers' Option Exercise Strategies 175
Proof See Appendix.▪
The results Et
o
L
<Et
e
L
and Et
o
F
<Et
e
F
in Corollary 3 confirm our
expectation that when developers collude on rents (which simultaneously optimizing
their profits), they are able to start the construction earlier than if they have to
ascertain full occupancy. This is true because the rental level at which the developers
collude provides the highest total revenue to them when compared with the rental
levels at other occupancy levels.
Corollary 3 also indicates that the construction time disparity is negatively
affected by the demand elasticity b. This is true because the trigger shocks are
decreasing in bunder the market clearance condition, but are increasing in bunder
the rent collusion condition. This outcome is not surprising. Any demand loss due to
an increase in the sticky rent is less significant when demand is less elastic. Given
this, the cost of collusion is reduced, while the incentive to build early increases.
Furthermore, the results that the disparities in construction are positively influenced
by the existing space Mconfirm our earlier findings. A larger existing supply is more
likely to encourage property developments when developers can collude on rents.
The mathematical interpretation is simple. The trigger shocks are decreasing in M
under the rent collusion condition, but are unaffected by Munder the market
clearance condition.
Conclusion
The persistence of overbuilding in real estate market cycles is rationalized in our real
options model where developers do not reduce rent to reach a full occupancy level. In
particular, we derive the optimal rental rate at which developers collude, the optimal
occupancy rate, and the critical values of demand shocks that trigger developments in
equilibrium. Our sticky-rent based real options model performs better than the
traditional market-clearance based real options models (such as Grenadier, 1996, and
Wang & Zhou, 2006) in explaining the overbuilding puzzle. Our real-options based
model also performs better than the static sticky rent model (by Wang & Zhou,
2000) in its ability to characterize dynamic developments and developers’behaviors.
Our conclusion on demand volatility contradicts that reported by Grenadier (1996).
We find that a high demand volatility actually delays the speed of developments
(rather than increases the speed of developments). We also find that, in cooperative
strategic games where developers collude on rental rates, a high demand elasticity
will discourage development. This finding contradicts the result reported in market-
clearance models such as Wang and Zhou (2006). In addition, a large existing supply
makes the real estate market insensitive to the new supply, which in turn increases
the speed of developments.
The impacts of sticky rental rates on investment decisions are not confined to real
estate markets. In fact, the models derived in this study can be applied to other types
of markets. Specifically, our model demonstrates that the investment decisions of
any industry with few suppliers (where collusion on the output price can occur more
easily) could differ from other industries where the prices of products adjust
promptly to the level of new supply.
176 R.N. Lai et al.
Acknowledgements We thank João Duque, John Erickson, David Geltner, John Glascock, Robert Van
Order, and participants of the 2005 Cambridge-Maastricht Symposium for their helpful comments. The
authors are solely responsible for any remaining errors in the paper.
Appendix
Proof of Proposition 1 We follow the standard procedure by guessing that the
Follower’s solution to Eq. 5takes the form FXðÞ¼AX b. Equating FX
e
F
to
condition 10b and F0Xe
F
¼bAX
e
F
b1to condition 10c, we derive the value of the
development opportunity at any level of demand shock as
FXðÞ¼
erμðÞδ
rμðÞ
cX e
F1
bQ
I
hi
X
Xe
F
b
if X<Xe
F;
erμðÞδ
rμðÞ
cX 1
bQ
Iif XXe
F;
8
<
:ðA:1Þ
where
Xe
F¼b
cb1ðÞ
1
bQþermðÞdrmðÞI
is the trigger point that prompts the Follower to start construction. Substituting the
differentials of FXðÞ¼AX binto Eq. 6, we have
1
2s2b2þm1
2s2
br¼0;
which generates
b¼1
2m
s2þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
m
s21
2
2
þ2r
s2
s:
To obtain the Leader’s strategy, notice that she/he enjoys perpetual rental earning of
L1XðÞ¼
ermðÞd
rmðÞ
cX 1
bQL
IðA:2Þ
before the Follower offers any rental units. By the time the Follower supplies rental
units at some time unknown to the Leader because Xe
Fis reached, the Leader will
lose the higher rent of RX tðÞ½¼cX tðÞ1
bQLand instead earn a diluted perpetual
rent of RX
e
F
¼cX e
F1
bQfrom then on (recall that Q¼QLþQF). The change in
rent, L
2
(X), will behave similarly as in Eq. 6, that is,
1
2s2X2d2L2
dX2þmXdL2
dX rL2¼0;
and the change in perpetual rental flow of
ermðÞd
rmðÞ
cX e
F1
bQcX tðÞ1
bQL
Stickiness of Rental Rates and Developers' Option Exercise Strategies 177
becomes the boundary condition to the partial differential equation. With similar
approach adopted for Eq. A.1, the solution becomes
L2XðÞ¼
ermðÞd
rmðÞ
cX e
F1
bQcX 1
bQL
X
Xe
F
b
:ðA:3Þ
Combining both rental values in Eqs. A.2 and A.3, the value of the construction
opportunity of the Leader at any demand shock level follows
LXðÞ¼
erμðÞδ
rμðÞ cX 1
bQL
1X
Xe
F
b
þcX e
F1
bQ
X
Xe
F
b
Iif X<Xe
F;
erμðÞδ
rμðÞ
cX 1
bQ
Iif XXe
F:
8
<
:ðA:4Þ
Note that the second equation is identical to that of the Follower in Eq. A.1, which
indicates simultaneous developments.
The best time for the Leader to start construction can be determined as follows. In
market equilibrium, a developer is indifferent to building now or building later (that
is, being a Leader or a Follower) if and only if the values of her/his construction
opportunity at both times are identical to her/his counterpart, that is, L(X)=F(X).
Otherwise, both developers will try to preempt the market in order to occupy the
market share as early as possible. Following this reasoning, there exists an Xe
L2
0;Xe
F
at which one developer would start construction and become the Leader.
This is obtained by setting LX
e
L
¼FX
e
L
, which generates
Xe
L¼1
c
1
bQLþermðÞdrmðÞI
:ðA:5Þ
Given that b
b1>1 is always true, it is easy to see that Xe
L<Xe
F.▪
Proof of Corollary 1 From Eq. 11 we know that
@Xe
L
@σ¼0;and ðA:6Þ
@Xe
L
@b¼QL
b2c<0:ðA:7Þ
Hence, from Eq. 13, we derive
@Et
e
L
@σ¼σln X e
L
ln X t0
ðÞðÞ
μ1
2σ2
2>0;and ðA:8Þ
@Et
e
L
@b¼1
Xe
Lμ1
2σ2
@Xe
L
@b<0:ðA:9Þ
178 R.N. Lai et al.
In addition, from Eq. 12, we have
@Xe
F
@s¼ Xe
F
bb1ðÞ
@b
@s>0;ðA:10Þ
where @b
@s¼2m
s31ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1þ
r
m2rmðÞ
m
s21
2
2
þ2r
s2
s
2
43
5<0;and,
@Xe
F
@b¼ bQ
b1ðÞb2c<0;
ðA:11Þ
Hence, from Eq. 13, we derive
@Et
e
F
@σ¼σln X e
F
ln X t0
ðÞðÞ
μ1
2σ2
2þ1
Xe
Fμ1
2σ2
@Xe
F
@σ>0;and ðA:12Þ
@Et
e
F
@b¼1
Xe
Fμ1
2σ2
@Xe
F
@b<0:ðA:13Þ
Finally, from Eq. 14, we have
@Ete
LF
@σ¼
@Xe
F
@b@b
@σ
Xe
Fμ1
2σ2
þσln Xe
F
ln Xe
L
μ1
2σ2
2>0;ðA:14Þ
given @b
@σ<0and @Xe
F
@b<0, which can be easily seen from Xe
F¼1
c11
b
ðÞ
½1
bQþerμðÞδrμðÞI,and
@Ete
LF
@b¼ berμðÞδrμðÞIQF
b2c2b1ðÞμ1
2σ2
Xe
FXe
L
<0:ðA:15Þ
▪
Proof of Proposition 2 To obtain the optimal strategies of the developers, first notice
that the optimal effective rental rate for the Follower from expression (20)is
Stickiness of Rental Rates and Developers' Option Exercise Strategies 179
RF*¼1vðÞMþaX o
F
½
2
4bMþQðÞ
, where Q¼QLþQF. With the same approach in Proposition 1,
the boundary conditions in deducing optimal Xo
Fare modified to
FX
o
F
¼ermðÞd1vðÞMþaX o
F
2
4brmðÞMþQðÞ
I;ðA:16aÞ
F0Xo
F
¼ermðÞda1vðÞMþaX o
F
2brmðÞMþQðÞ
:ðA:16bÞ
With a guess that the Follower’s solution to Eq. 5takes the form FXðÞ¼AX band
subject to conditions A.16a and A.16b, the value of the development opportunity
becomes
FXðÞ¼
erμðÞδ1vðÞMþaX o
F
2
4brμðÞMþQðÞ
I
"#
X
Xo
F
b
if X<Xo
F;
erμðÞδ1vðÞMþaX½
2
4brμðÞMþQðÞ
Iif XXo
F;
8
>
>
>
>
<
>
>
>
>
:
ðA:17Þ
and the corresponding optimal trigger point Xo
Fis
Xo
F¼1
ab2ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4bb2ðÞerμðÞδIrμðÞbMþQðÞþM21vðÞ
2
qb1ðÞ1vðÞM
:
Substituting into Eq. 6for FXðÞ¼AX b, we find that bis identical to that in the case
of market clearance situation (b>2 is a necessary condition for the equation to be
valid).
To obtain the optimal strategy of the Leader, notice from Eq. 18 that before the
Follower enters the market, the Leader (and all other current participants in the
market) should be requesting an optimal rigid rate of RL*¼1
2b1vðÞMþaX o
L
, so that
the corresponding effective rental rate is RL*¼kL*RL*¼1vðÞMþaXo
L
½
2
4bMþQL
ðÞ
. Following the
approach adopted in “Developers’Game with a Market Clearance Condition,”the
Leader’s profit function is L
1
+L
2
where
L1¼ermðÞd
rmðÞ
1vðÞMþaX o
L
2
4bMþQL
ðÞ
I;
and
L2¼ermðÞd
rmðÞ
1vðÞMþaX o
F
2
4bMþQðÞ
1vðÞMþaX½
2
4bMþQL
ðÞ
"#
X
Xo
F
b
(again Q¼QLþQF), when the Follower has entered the market. Note that the term
in the parentheses of L
2
must be negative because the profit without the Follower
must be higher than that with her/his existence. That is, there must be incentive for
180 R.N. Lai et al.
developers to enter the market first to become the Leader. There exists a unique
demand shock Xo
Lthat results in developers being indifferent to being Leader or
Follower. This is obtained by setting LX
o
L
¼FX
o
L
, which generates
Xo
L¼1
affiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4ermðÞdIrmðÞbMþQL
ðÞ
q1vðÞM
:ðA:18Þ
To show the existence of Xo
L20;Xo
f
, we make use of the fact that C−D>0if
C2D2¼CþDðÞCDðÞ>0givenC> 0 and D> 0 for some arbitrary constants
Cand D. In other words, combining Xo
Land Xo
Fand rearranging, we have
Xo
F
2Xo
L
2¼1
a2b2ðÞ
2"2M1vðÞb1ðÞ
"ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
M21vðÞ
2
qþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
b2ðÞ
4GL
b1ðÞ
2
s
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
bb2ðÞGþM21vðÞ
2
q##þbGb2ðÞGL
½
b2ðÞ;
where G¼4ermðÞdIrmðÞbMþQðÞand GL¼4ermðÞdIrmðÞbMþQL
ðÞ.Itis
obvious that G>G
L
, which implies the last term on the right-hand side is positive.
Thus, as long as we confirm that ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
M21vðÞ
2
qþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
b2ðÞ
4GL
b1ðÞ
2
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
bb2ðÞGþM21vðÞ
2
q
is positive, we
can show that Xo
F
2Xo
L
2>0, which leads to Xo
F>Xo
L. We again apply the same
concept that C−D>0ifC2D2¼CþDðÞCDðÞ>0givenC> 0 and D>0,
and obtain
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
M21vðÞ
2
qþffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
b2ðÞ
4GL
b1ðÞ
2
s
"#
2
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
bb2ðÞGþM21vðÞ
2
q
2
¼b2ðÞM2"ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
b2ðÞ
216erμðÞδrμðÞb1vðÞ
2I
M1þQL
M
b1ðÞ
2
s
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
b24erμðÞδrμðÞbI
M1þQ
M
2
s#þb2ðÞ
4GL
b1ðÞ
2>0;
and this is true given that I(M+Q
L
)(inG
L
) is far greater than I
M1þQL
M
and
I
M1þQ
M
(in the big parenthesis). This means that Xo
F
2Xo
L
2>0, and hence
that Xo
F>Xo
L.
Comparing the two demand shock formulae, we see that one main difference lies
on the presence of bin Xo
Fbut not Xo
L. It is therefore worth to examine the effect of b
on Xo
F. Taking the derivative, we have
@Xo
F
@b¼ Xo
F
b2ðÞ
M1vðÞ
ab2ðÞ
1b1ðÞ
1vðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
b2ðÞbM2
BþM2
B
21vðÞ
2
q
0
B
@1
C
A;ðA:19Þ
Stickiness of Rental Rates and Developers' Option Exercise Strategies 181
where B¼4be rmðÞdrmðÞbI M þQðÞ. Given r,μand vfar smaller than 1, and
hence M2
B¼1
4be rμðÞδrμðÞbI
M1þQ
M
ðÞ
will be very large, the second term in the big parenthesis
will be very small and we have @Xo
F
@b<0. ▪
Proof of Corollary 2 From Eq. 21, we have
@Xo
L
@b¼1
ab ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ermðÞdIrmðÞbMþQL
ðÞ
q
>0;ðA:20Þ
and given r,μand vfar smaller than 1, we have
@Xo
L
@M¼1
affiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ermðÞdrmðÞbI
MþQL
ðÞ
s1vðÞ
!
<0;ðA:21Þ
as long as M+Q
L
are larger than I, which is usually true. Then, from Eq. 18, we have
@Ro
L
@b¼ 1
2b2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
erμðÞδIrμðÞbMþQL
ðÞ
q
<0;ðA:22Þ
@Ro
L
@M¼1
2b
1
MþQL
ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ermðÞdIrmðÞbMþQL
ðÞ
q
>0:ðA:23Þ
Furthermore, we have
@Xo
L
@σ¼0;ðA:24Þ
@Ro
L
@s¼a
2b
@Xo
L
@s¼0;ðA:25Þ
Then, from definition (13), we can derive
@Et
o
L
@b¼1
Xo
Lμ1
2σ2
@Xo
L
@b>0;
@Et
o
L
@M¼1
Xo
Lμ1
2σ2
@Xo
L
@M<0;
and
@Et
o
L
@σ¼σln X o
L
ln X t 0
ðÞðÞ
μ1
2σ2
2þ1
Xo
Lμ1
2σ2
@Xo
L
@σ>0:
182 R.N. Lai et al.
In the Follower’s case, for simplicity, we assume Y¼2berμðÞδIrμðÞbMþQðÞ
and Z¼1
1vðÞ
2bb2ðÞermðÞdIrmðÞb
, and from Eqs. 22 and 18,
@Xo
F
@b¼Y
ab ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2b2ðÞYþ1vðÞ
2M2
q>0;ðA:26Þ
@Ro
F
@b¼1
2b2b2ðÞ
b1vðÞ
Yb2ðÞþ1vðÞ
2M2
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2b2ðÞYþ1vðÞ
2M2
q
0
B
@1
C
A<0; ðA:27Þ
In addition, we have
@Xo
F
@M¼1vðÞ
ab2ðÞ
Zþ1vðÞM
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
21vðÞZMþQðÞþ1vðÞ
2M2
qb1ðÞ
0
B
@1
C
A<0;ðA:28Þ
which is proved as follows. As the sign of @Xo
F
@Mdepends only on the sign of the terms
in the big parentheses given b> 2 and r,μand vfar smaller than 1, we rewrite these
terms as Zþ1vðÞM½b1ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
21vðÞZMþQðÞþ1vðÞ
2M2
p
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
21vðÞZMþQðÞþ1vðÞ
2M2
p. Applying the concept that C−D<0
if C2D2¼CþDðÞCDðÞ<0 given C> 0 and D> 0 for some arbitrary
constants Cand D, we have
Zþ1vðÞMðÞ
2b1ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
21vðÞZMþQðÞþ1vðÞ
2M2
q
2
¼1vðÞMþZðÞ
2b1ðÞ
21vðÞ
2M2þ2Z1vðÞMþQðÞ
¼1vðÞ
2M2þ2Z1vðÞM
1b1ðÞ
2
þZ2b1ðÞ
22Z1vðÞQ
<0;
given that b>2andZ<2(b−1)(1 −ν)Q(due to the small r,μand v). This result
implies that Zþ1vðÞM½b1ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
21vðÞZMþQðÞþ1vðÞ
2M2
q<0and hence
@Xo
F
@M<0.
Also, from Eq. 18, we have
@Ro
F
@M¼1vðÞ
2bb2ðÞ
Zþ1vðÞM
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
21vðÞZMþQðÞþ1vðÞ
2M2
q1
0
B
@1
C
A<0;ðA:29Þ
which can be proved with a similar approach that shows
Zþ1vðÞM<ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
21vðÞZMþQðÞþ1vðÞ
2M2
q:
Stickiness of Rental Rates and Developers' Option Exercise Strategies 183
Then, from definition (13), we can derive
@Et
o
F
@b¼1
Xo
Fm1
2s2
@Xo
F
@b>0;
and
@Et
o
F
@M¼1
Xo
Fm1
2s2
@Xo
F
@M<0:
To facilitate discussion on the time lag between the two developments, we assume
that A¼ermðÞdrmðÞbI. Note that given r,μand vfar smaller than 1, while M
very large and larger than I, it must be that A<<M.
From Eqs. 21 and 22, we have
Xo
FXo
L¼1vðÞMþb2ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4AMþQL
ðÞ
p
þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4b2ðÞbAMþQðÞþ1vðÞ
2M2
q
ab2ðÞ :
Correspondingly,
@Xo
FXo
L
@b¼A
ab ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
MþQL
A
rþ2b
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4b2ðÞbA
MþQðÞ
þ1vðÞ
21
1þQ
M
2
s
0
B
B
B
B
@
1
C
C
C
C
A
<0;
ðA:30Þ
because A<<M+Q
L
makes the first (negative) term significantly dominate the second
(positive) term in the outermost parentheses on the right-hand side.
Then from the definition in Eq. 14, we have
@Eto
LF
@b¼1
m1
2s2
Xo
FXo
L
@Xo
F
@b@Xo
L
@b
Xo
FþXo
LXo
F
@Xo
F
@b
<0;ðA:31Þ
given @Xo
F
@b@Xo
L
@b¼@Xo
FXo
L
ðÞ
@b<0 (see result A.30), Xo
LXo
F<0 and @Xo
F
@b>0:In
addition,
@Xo
FXo
L
@M¼1
ab2ðÞ
1vðÞþ 2b2ðÞbA
Mþ1vðÞ
2
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4b2ðÞbA
M1þQ
M
þ1vðÞ
2
qb2ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
A
MþQL
s
0
B
@1
C
A:
ðA:32Þ
184 R.N. Lai et al.
To study the sign of @Xo
FXo
L
ðÞ
@M, notice that the term in the large parenthesis on the
right hand side of the equation
1vðÞþ 2b2ðÞbA
Mþ1vðÞ
2
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4b2ðÞbA
M1þQ
M
þ1vðÞ
2
qb2ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
A
MþQL
s
<1vðÞþ
2b2ðÞbA
Mþ1vðÞ
2
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2b2ðÞbA
Mþ1vðÞ
2
qb2ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
A
MþQL
s
¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2b2ðÞfb
pA
Mþ1vðÞ
2
1vþb2ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
A
MþQL
s
!
:
With the same concept that C−D<0ifC2D2¼CþDðÞCDðÞ<0, and
given A<<M, the last expression can be proved to be negative, which implies that
@Xo
FXo
L
ðÞ
@M<0. Since from Eq. 14 Eto
LF
and Xo
FXo
L
in general move in the same
directions as Mchanges, we have @Eto
LF
ðÞ
@M<0.
Finally,
@Eto
LF
@σ¼σln Xo
F
ln Xo
L
μ1
2σ2
2þ
Xo
L
@Xo
F
@σXo
F
@Xo
L
@σ
hi
μ1
2σ2
Xo
FXo
L
>0;ðA:33Þ
because @Xo
F
@s>0and@Xo
L
@s¼0. ▪
Proof of Corollary 3 Again, to facilitate discussion, we assume that A¼erμðÞδ
rμðÞbI, and we have A<<Mgiven r,μand vfar smaller than 1 while Mvery large
and larger than I.
Following Eqs. 11 and 21, we have
Xe
LXo
L¼1
aM1vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4A
M1þQL
M
s
!
þQLþA
!
>0;
given A<<M.
Xe
FXo
F¼
b2ðÞbQþAðÞþb1ðÞ
21vðÞM
b1ðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4b2ðÞbAMþQðÞþ1vðÞ
2M2
q
ab2ðÞb1ðÞ >0;
which can be proven using similar approach as before. That is, by b2ðÞbQþAðÞþð
b1ðÞ
21vðÞMÞ2b1ðÞ
2ðffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4b2ðÞbAMþQðÞþ1vðÞ
2M2
qÞ2
>0:These results in-
Stickiness of Rental Rates and Developers' Option Exercise Strategies 185
dicate that Xe
LXo
L>1, and Xe
FXo
F>1. Then with Eq. 13, we can derive
Et
e
L
Et
o
L
¼ln Xe
L
ln Xo
L
μ1
2σ2¼ln Xe
LXo
L
μ1
2σ2>0;
and
Et
e
F
Et
o
F
¼ln Xe
F
ln Xo
F
μ1
2σ2¼ln Xe
FXo
F
μ1
2σ2>0:
Given A
Mvery small, we can also derive
@Xe
LXo
L
@b¼1
ab ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
AMþQL
ðÞ
p1þffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
A
MþQL
s
!
<0;ðA:34Þ
and
@Xe
LXo
L
@M¼1
a1vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
A
MþQL
s
!
>0;ðA:35Þ
@Xe
FXo
F
@b¼1
ab b1ðÞ
bA12b1ðÞMþQðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4b2ðÞbAMþQðÞþ1vðÞ
2M2
q
0
B
@1
C
A<0;ðA:36Þ
because it can be shown that 2b1ðÞMþQðÞ
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4b2ðÞbAMþQðÞþ1vðÞ
2M2
q>0;
and
@Xe
FXo
F
@M¼1
ab2ðÞ
b1ðÞ1vðÞ
2b2ðÞbA
M2þ1vðÞ
21
M
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4b2ðÞbA
M1þQ
M
þ1vðÞ
2
q
0
B
@1
C
A>0:
ðA:37Þ
Again from Eq. 13,Et
e
L
Et
o
L
and Xe
LXo
Lshould in general move in the
same directions when bor Mchanges, and so do Et
e
F
Et
o
F
and Xe
FXo
F.▪
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