Journal of Economic Growth, 1:125-142 (March, 1996)
9 1996KluwerAcademicPublishers,Boston.
Social Conflict and Growth
JESS BENHABIB
Department of Economics, New York University, New York, NY 10003
ALDO RUSTICHINI
CORE, Universite Catholique de Louvain, Louvain La Neuve, 1348, Belgium
Despite the predictions of the neoclassicaltheory of economic growth, we observethat poor countries have invested
at lower rates and have not grown faster than rich countries. To explain these empirical regularities we provide
a game-theoretic model of conflict between social groups over the distribution of income. Among all possible
equilibria, we concentrate on those that are on the constrained Pareto frontier. We study how the level of wealth
and the degree of inequality affects growth. We show how lower wealth can lead to lower growth and even to
stagnation when the incentives to domestic accumulation are weakened by redistributive considerations.
Keywords: dynamic games, growth, social conflict
JEL Classification: D74, 040
1.
Introduction
Neoclassical growth theory predicts that poor countries, because of the law of diminishing
returns, grow at faster rates than rich countries. This inverse relation between wealth
levels and growth rates should further be strengthened by the diffusion of technology and
the opportunities for catching up. Yet, despite concerted efforts at faster development,
we observe that poor countries have invested at lower rates, exhibited more intense social
conflict and political instability, and consequently have not grown faster than rich countries.
The empirical relationship between income levels and growth rates is fiat and possibly
hump-shaped, not downward sloping. 1 One possible explanation for these results has been
given by theories of endogenous growth that appeal to human capital to eliminate labor as
a fixed factor, or by introducing elements of increasing returns (see Lucas, 1988; Romer,
1986, 1990). A n alternative approach known as the c o n d i t i o n a l c o n v e r g e n c e hypothesis
(see Barro, 1991; Mankiw, Romer, and Weil, 1992; Levine and Renelt, 1992) suggests that
the lower growth rates observed in poorer countries are essentially due to lower rates of
accumulation in physical and human capital. W h e n factor accumulations or savings rates are
taken into account, the predicted negative relation between growth rates and initial income
levels is reestablished. Indeed, it has been observed that investment rates in physical and
human capital (primary schooling) are positively correlated with income levels (see Fisher,
1991). Furthermore, investment rates show a robust negative correlation with various
measures of political instability (see Barro, 1991; Levine and Renelt, 1992; Venieris and
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BENHABIB AND RUSTICHINI
Gupta, 1986), and there is a negative relationship between measures of political instability
and levels of income (see Alesina and Perotti, 1993; Londregan and Poole, 1990). The crosscountry evidence suggests then that poorer countries are more prone to political instability,
have lower investment rates, and consequently may not have realized their growth potential
to catch up with rich countries.
In this paper we offer a model that can explain why poor countries have tended to invest
and accumulate at rates lower than the rich countries. We pursue an alternative gametheoretic course that emphasizes the relationships between levels of wealth, social and
political conflict, and incentives for accumulation. As such our work is indirectly related
to papers by Persson and Tabellini (1994), Alesina and Rodrik (1994), Grossman (1991),
and Tornell and Velasco (1992).
We have in mind a situation where organized social groups can capture, or attempt to capture, a larger share of the output either by means of direct appropriation or by manipulating
the political system to implement favorable transfers, regulations, and other redistributive
policies. 2 Depending on the country, these groups may represent, among others, organized
labor, industrial and business associations, the military, the bureaucracy, or racial, ethnic,
and tribal groups. 3 Such redistributive and expropriative activities undertaken by social
groups can create significant disincentives to accumulate, which as we show below, can be
stronger at lower levels of wealth than at higher ones, so that poorer countries grow more
slowly or even stagnate at lower levels of wealth. We obtain these results in our model
without having to rely on the alternative and probably complementary framework that requires nonconvexities or threshold effects in the production technology (see, for example,
Lucas, 1988; Romer, 1986, 1990; Azariadis and Drazen, 1990).
To capture the empirical relationship between wealth and growth discussed above, we
use a simple dynamic game framework. Social groups are modeled as players who independently choose a consumption level; the residual output, if any, becomes the capital or
the productive resource in the following period. We consider equilibrium paths of accumulation in which players receive utilities that are at least as high as those that they could
obtain by defecting: that is, by appropriating higher immediate consumption levels and
suffering some retaliation later on. (For a related framework of analysis, see Marcet and
Marimon, 1990; Chari and Kehoe, 1990; Tornell, 1992.) We focus, however, on those
subgame-perfect equilibria that are second best--that is, on the subset of subgame-perfect
equilibria that lie on the constrained Pareto frontier. There are three main reasons for this
choice. First, it is conceivable that those are, in fact, the equilibria we observe because institutional arrangements and social norms that select an efficient outcome among equilibria
may develop. 4 Second, as we discuss later, these are equilibria in which the economy grows
at the fastest rate; so they provide an upper bound to the growth rate. Finally, in this way
we obtain an indirect measure of the effects of the strategic behavior of groups: it is at least
as large as the difference between first and second best. Within the set of second best, we
analyze the effects of wealth on growth and on steady-state income levels.
Whether high or low levels of wealth depress investment and growth rates critically
depends on the curvatures of technology and preferences. To illustrate these possibilities
we study two opposite cases. At first we consider the case in which lower wealth leads to
lower growth and sometimes, though not necessarily always, to a "growth trap." This case
SOCIAL CONFLICT AND GROWTH
127
is likely when there are sufficiently high diminishing returns in utility: when wealth levels
are high, appropriating a large amount of consumption, at the expense of future retaliation,
becomes less attractive. At lower wealth levels however, when consumption is low and
marginal utility is high, the opposite may be true, especially if the marginal product of
capital does not become high enough to deter defection with a high level of consumption.
In the extreme, we may observe "growth traps?' Even though first-best policies lead to
growth, along second-best equilibria growth may have to be slower or may not even be
possible at low wealth levels because of incentive constraints: the accumulation of wealth
by one player can lead to appropriation and to high consumption by other players and
therefore may not be sustainable as an equilibrium.
Another possibility is for incentive constraints to bind at high wealth levels and not at
low ones. This type of case occurs when marginal utility does not diminish too strongly
while the marginal product of capital does. Defecting with a large amount of consumption
at high levels of wealth may now become attractive. Because of diminishing returns in
production however, capital may be too precious at low levels of wealth, and players may
initially follow first-best policies of accumulation. Inefficiency sets in at higher levels of
wealth and first-best policies may have to be abandoned as the incentives for appropriation
grow and redistributive pressures increase. The possibility that inefficiencies are associated
with stable and wealthy economies in which organized groups have had the time to mature
and exert redistributive pressures has been suggested by Mancur Olson (1982).
The discussion above and the theoretical analysis in the subsequent sections suggest
that structural and specific aspects of the economy, as modeled by the preferences and
technology, determine whether the strategic behavior of interest groups is likely to diminish
growth at high levels or at low levels of wealth. Whether group conflict and strategic
behavior can lead to slow growth at high or low wealth levels, or maybe even at both high
and low wealth levels, remains therefore an empirical matter. We illustrate the theoretical
possibilities in Sections 5 and 6 below.
In Section 2 we show that when incentive constraints are binding, the fastest-growing
subgame perfect equilibrium is the symmetric (egalitarian) second best. For instance,
if incentive constraints are binding at low levels of wealth, then the growth rate of the
symmetric (egalitarian) second-best equilibrium sets an upper bound to the growth rates
at low wealth levels. Growth rates on all other equilibria, including the nonsymmetric
or inegalitarian second best, must be even lower. Our model therefore also indicates that
for any given level of wealth, there is a tradeoff between growth and inequality, where
inequality is measured by the disparities of consumption rates and welfare levels. (For
a similar view based on credit market imperfections, see Galor and Zeira, 1993.) High
rates of accumulation in economies with pronounced and persistent inequalities may not
be sustainable because the disadvantaged groups can undertake redistributive actions or
exert redistributive pressures that discourage domestic investment. The political consensus
necessary for efficient growth may not be attainable if income inequality is too severe.
Recent empirical work has confirmed the inverse relationship of income inequality with
investment and growth (see, for example, Venieris and Gupta, 1988; Alesina and Rodrik,
1994; Persson and Tabellini, 1994).
Our paper is organized as follows. The next section sets up the problem in a general
128
BENHABIB AND RUSTICH1NI
framework. Section 3 works out a simple and illustrative example of a second-best problem
where incentive constraints retard growth but accumulation rates do not depend on wealth.
Section 4 provides some general conditions under which a political "growth trap" occurs
without having to explicitly compute the "second best." Section 5 computes an explicit
example of a case where growth is slow relative to first-best levels only when wealth levels
are low. It also provides an example of a discontinuous value function. Section 6 illustrates
the "Olson" case where first-best policies are optimal at low stock levels but cannot be
sustained at high stock levels. Section 7 concludes with a brief overview.
2.
The Second-Best Problem
We consider two players characterized by two concave and strictly increasing utility functions Ui, i = 1, 2, and a common discount factor fl 6 (0, 1). kt represents the capital stock
at time t. The production function f is concave, increasing, and f ( 0 ) >_ 0. The feasible
paths of the consumption sequences must satisfy f (kt) - c] - c 2 < kt+l, and c ti > 0 ,
t = 0, 1 , . . . ; i = 1, 2. In our game, histories at time t are sequences of consumption pairs
ht = (c 11, cl2,. .. , c], c2t), and strategies are maps from histories to consumptions. For a
given initial stock k, the second-best value is defined by
to
Vsb(k) =---sup E
flt[~ U1 (c~) -4- ot2U2(ct2)],
(1)
t=O
where the supremum is taken over the sequences (c], c2t)t>_oof subgame perfect equilibrium
(SPE) outcomes and or1, a2 > 0.
The purpose of this section is to prove that the second best is achieved over a smaller
set of SPE. To avoid ambiguities, we describe in detail how the allocation of consumption
is regulated. It will be useful to distinguish between attempted consumption and actual
consumption (the first is the consumption a player is trying to get, the second is what
he actually gets under the allocation rule). For a given capital stock k and attempted
consumptions cl and c2, the actual allocated consumption is
if Cl + C2 <__.f ( k ) or cl < f ( k ) / 2
Cl
A 1(c l,
C2,
k) =
f (k)
- s
f(k)/2
if cl + c2 > f ( k ) and Cl > f ( k ) / 2 > c2
if ca, c2 > f ( k ) / 2
and similarly for A2. Note that if e2 -~< f ( k ) / 2 , then Al (cl, C2, k) = min{cl, f ( k ) - c2}.
Since the utility function of both players is strictly increasing, the following pair of
strategies, which we call fast consumption strategies, constitutes an equilibrium for all
values of the capital stock k:
6~(k)=?2(k) = f(k).
Note in fact that in this case the allocation rule gives A 1 (C1, C2, k) = A2 (c2, C1, k) = f (k)/2
to both players. Also note that if the second player attempts to consume f ( k ) , for any choice
SOCIAL CONFLICT AND GROWTH
129
of c1 the capital stock in the next period is zero. So by reducing Cl the first player can only
reduce his payoff. 5
Under the allocation rule described above, the worst SPE is easily described. This allows
us to utilize the worst equilibrium in order to sustain any other SPE with trigger strategies.
Note that one may also arbitrarily choose a simple SPE--for example, the interior Markovian
one under which the sum of attempted consumptions never exceeds output--and then study
the set of SPE that are enforcable with trigger strategies using that Markovian SPE as a
threat.
As noted above, it is clear that the pair (~1, ~2) is a SPE, since the utility functions of the
players are strictly increasing. The value of this equilibrium to player i is given by
tx~
~)i(k) = y ~ ~tUi(Ai(cl(kt),
c2(kt), kt)),
i = 1, 2,
t=0
where ko = k, kt+l = f ( k t ) - Al(Cl(kt), c2(kt), kt) - A2(cl(kt), c2(kt), kt), t > 0. Of
course, if f ( 0 ) = 0, the above summation reduces to U/(f(k)/2). A trigger strategy pair
is described by an agreed consumption path (ct,
1 ct2)t>o and the threat of a shift to a fastconsumption equilibrium after the first defection is detected. The individual rationality
constraint for player i on an outcome path is the condition
~ ~tU(c~) _>~i(k).
t
Clearly, in a SPE, the outcome of the equilibrium of any subgame satisfies this inequality.
Consider now a trigger strategy equilibrium. For any capital stock k and equilibrium
consumption c of the other player, the value of defection is the value for a player of
deviating optimally--that is,
vD(k, c) = Max{wD(k, c), ~i(k)},
wD (k, C) =
max
U ( c ' ) + f l U ( - ~ f1( f ( k )
O<_c'<_f (k)--c
_ c - c ' ) ) - - t - l f l m2 U ( f ( O ) / 2 )
'
(2)
and
kl = f ( k ) - c - Ai(k, c, c'),
kt+l = f ( k t ) - Al(~l(kt), c2(kt), kt) - A2(?l(kt), c2(kt), kt),
t >_ 1.
(3)
Note that this optimization problem can be expressed without the maximization operator
in defining vD by simply adding the constraint v~ (k, c) > vi (k). We denote by c ~ (k, c)
the consumption giving the optimal deviation: in the games we consider such optimal
consumption exists and is unique.
The following lemma is clear. We state and prove it for completeness.
L e m m a 2.1: Let (c] , C2)t>O be the outcome of a SPE--~, say. Then the trigger strategy
pair with this agreed consumption path, ~' is an SPE.
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BENHABIB AND RUSTICHINI
Proof
For any history ht, we denote vi(ht) the value to the ith player of the equilibrium in ~ starting with ht. We only need to consider equilibrium histories ht-1 =
(C~, c l , 9
1 l, Ct_l).
2
ct_
Let kt be the capital stock. We claim that ct2 is an optimal choice
for player 2 next period, in ~'. The best alternative choice is cD(kt, c 1) -- c D. In the
equilibrium ~ such a choice would give him a payoff of Uz(c D) plus the equilibrium value
of the subgame starting at (ht, c 1, cD). In the equilibrium of this subgame, the individual
rationality constraint is satisfied, so our claim follows from the expression below:
9
U2(c2t) -t- flv2(ht, c], c2t) > U2(c D) -b flv2(ht, c t1, CD)
>__ U2(c o) d- fl~)2(f(kt) - c t1
=
__ C D )
(k,,
9
It follows that the supremum in the definition of a second best is the same as the supremum
over trigger strategy equilibria. As a first implication of this reduction we prove that the
second-best value is in fact achieved. We turn to this now. Let ~1, ct2 > 0 be weights
attached to the players. From what we have seen, the second best is the solution of the
problem:
Osb(k) ~
Isup
~
flt[OllUl(C~) -[- o~2U2(ct2)],
(4)
{(ct ,ct )t_>o} t
subject to f (kt) - clt - c2t >_ kt+l, and
~ ~ 1 7o6 ~t+iu.1(C{+i)>__vD(ki,cJ "')
i : 1,2 . . . . ;
j : 1,2 9
t
Below we refer to this as the second-best problem. It is easy to show that under mild assumptions a second-best solution exists and that the value function Vsb is uppersemicontinuous 6
(see Benhabib and Rustichini, 1991) 9
It is clear from equation (4) that there will be a second-best equilibrium for each set of
weights (oil, or2) and that the equilibrium will be symmetric when the weights are equal. The
proposition below establishes that when constraints are binding, a symmetric or egalitarian
second-best equilibrium is also the fastest growing subgame perfect equilibrium 9 Since in
the examples below we study the symmetric second best this proposition will be useful to
illustrate the extent to which growth is curtailed by incentive constraints across different
equilibria 9
Proposition 2.1: For a given k, let (c t1, c2)t_>0
t
be a second-best equilibrium outcome,
starting from k, which is symmetric and such that vi(k) = vD(k, cr), f o r i = 1, 2. If
kl = f (k ) - cl - c2, and k~ is the next period capital stock f o r any other subgame perfect
equilibrium, then k~l < kl.
For a proof see Benhabib and Rusfichini (1991) 9
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SOCIAL CONFLICT AND GROWTH
3.
A Simple Example of Second-Best Equilibrium with No Wealth Dependence
We will start by exploring a simple case of a second-best equilibrium to illustrate how
growth rates may differ drastically between first-best and incentive constrained second-best
equilibria. This first example is simple because growth rates on equilibrium paths will
turn out to be independent of the levels of wealth--that is, of the capital stock. The more
interesting and complex cases will be studied later.
Let each of the two identical players in this example have an instantaneous utility function
given by U(c) = (1 - E ) - l c 1-" with 0 < E < 1, with discount rate 0 < fl < 1. Let the
production function be y = ak with a > 0. The total utility of each player among a
first-best equilibrium is described by the dynamic program
~(k) = Max0<c< 89
(1
-
E)--lc 1-E --}-flf)(y -- 2C).
(5)
The consumption function that solves this program is given by ~ = )vy, where
~. = ~1
1 (1-~)\
1 - ~ ; a --7- ) _> 0
(6)
and where we have imposed the restrictions a > 1, ~l/'aO-')/" < 1 to avoid negative
consumption levels and to ensure a well-defined value function. For any ;v > 0, the value
function is given by v(k) = s(~.)y O-E), where
(1 - E)-I;0 -"
s()0 = 1 -- fl(a(1 - - 2 ~ . ) ) 1 - ' "
(7)
We note for further use below that s is derived here for arbitrary 3. > 0, not only for the
first-best ~.
When a player defects against first-best play by his opponent, he must choose his consumption in the current period taking into account that trigger strategies will be enacted
subsequently. Optimal defection value is therefore
vD(k, ~(k))
=
Max0_<cD_<(l_~)y(1 - - E ) - l c l D -E
"-~ / ~ ( 1 -
6) - 1
(a((1-
~.)y -CD)/2)l--E,
(8)
where ~(k) = ~y. This value reflects the trigger strategy equilibrium in which, following a
defection, all output is consumed in equal shares by the two players. The optimal defection
policy for consumption against another player consuming Zy with L < 1/2 is given by
CD(k ,
Ly) ----M(1 - J~)y =
)vDy ,
where M = (( 2P-~
-) 1/~ ( 2 ) + 1)-1 < 1. The value of optimal defection is given by v D (k, Ly) =
SDy O-E), where
so = (1 -- L)l-~(1 -- E ) - I [ M 1-' + fl((1 -- M)a/2) 1-~]
=
(1
--
~.)I-E(1
--
E)-lM -'.
(9)
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BENHABIB AND RUSTICHINI
^ ^D
V V ~Vsb
~D
Vsb
k 1-
Figure 1.
For first-best policies to constitute an equilibrium, the value that they generate for each
player must dominate the values of defection at each point on the equilibrium path--that
is, v(k) > vO(k, ~(k)) for all k on the equilibrium path. As we illustrate later in examples,
however, v (k) and v ~ (k) can intersect so that first-best outcomes can be enforced from some
values of k but not from others, as discussed in Benhabib and Radner (1992) or Benhabib
and Ferri (1987).
A symmetric second-best equilibrium with incentive compatibility constraints will be
given by the solution to the following problem:
Vsb(k) = Max0<c<~ (1
-
E)--Ic 1-• "~ Vsb(ak -- 2C),
subject to Vsb(k) > vD(k, c).
Clearly, if s(L^) > sd(~^), then the first-best equilibrium is enforced. If, however, s(L^) <
Sd()C), then the second best must differ from the first best. The consumption function is
then given by c = Lsy, where ~-s < (1/2) is defined by s()~s) = sa(Ls) (for a formal proof
see Benhabib and Rustichini, 1991).
Figure 1 illustrates the second-best solution when incentive constraints are binding. The
solution is to find ~ , which equates the value for each player of following the consumption
policy C~b = )~y with the value of defecting from it. In other words, consumption must
be increased and accumulation slowed down to the point where defection is no longer
attractive. ~o in Figure 1 is the value of defecting against a player following first-best
strategies.
The following numerical values illustrate the effects of incentive compatibility constraints
on economic growth along the symmetric equilibrium. We set a ---- 3.3, /5 = 0.325
(implausibly high discounting, of course), and E = .5. For these values vD(k, ~(k)) > ~)(k)
for all k > 0, where ~(k) corresponds to the first-best values with policies c = Ly. We
compute ~. = 0.326, L~ ---- 0.349. These magnitudes imply that if the first best could
be sustained, the capital stock would perpetually grow at 15 percent. On the second-best
path, however, the economy grows at -0.0015 percent--that is, it contracts. Of course,
parameters were chosen to make this stark point. Slightly different parameters would allow
positive growth along the second-best equilibrium but at a slower rate than the first best.
SOCIALCONFLICTAND GROWTH
133
Of course, in some cases the first best may be enforcable as an equilibrium from all stocks
so that incentive constraints do not bind. We note that for the parameters above it is easy
to check that y - 2Csb(k) > 0 and y - ~(k) - CD(k) > 0 for all k > 0.
4.
Wealth Dependent Growth
In general, it is not at all easy to compute second-best equilibria even for simple problems.
For example, if we slightly alter the linear production function of the previous section
to y = ak -4- b, b > 0, it is no longer possible to find a constant )~ to equate v(k) and
on(k, c). In particular fi(k) and on(k, ~) may intersect at some k. If fi(k) > on(k, ~) and
k > k, first-best policies will be sustainable as equilibria for k > k. From initial conditions
below k where fi(k) < v ~
~(k)), it may be possible to construct "switching" equilibria
(which are not necessarily second best), along which growth occurs at a rate slower than
first-best rates until k is reached, and first-best policies are followed once k is attained.
In this section we will derive conditions under which the second-best growth rates will
be wealth dependent: in particular we will find general conditions under which first-best
growth rates are sustainable from high stocks, while growth is not at all possible from low
stocks because of incentive compatibility constraints. The intuition for the result is simple:
relative to first-best levels, consumption rates must be increased and accumulation slowed
to prevent defection. When stocks are low, consumption must be increased so much to
prevent defection that growth is no longer possible. Examples will follow.
P r o p o s i t i o n 4.1: Assume that f o r some k (1) f)(k ) < vO (k, ~(k ) ) and (2) f (k ) - 2~ < k,
where ~ is the least c such that U(c) + f l ~ ( f ( k ) - 2c) = vO(k, c). Then f ( k ) - 2c < k
f o r any c which is the first period consumption rate of a symmetric S P E (that is growth is
impossible). In particular this is true f o r second best equilibria.
Proof:
A s s u m e that
f(k)
- 2c > k; then clearly c < ?. But then, if v(k) is the value of
the equilibrium,
vO(k,c)
< v(k)
(10)
<_ U(c) + f l ~ ( f ( k ) - 2c)
(11)
< vO(k, c),
(12)
where (10) holds by definition of SPE, (11) holds because ~ > v, and (12) holds by the fact
that U(c') + t i f f ( f (k) - 2 # ) < vO(k, c') for every c ~ (~(k), ~); this interval is nonempty
because of the assumptions 1 and 2. We have derived a contradiction. We note that if a
as defined above does not exist, condition 2 can be taken to be trivially satisfied. Finally,
since the fastest growing SPE is the symmetric second best by Proposition 2.1, the result
applies to all SPE and all second best equilibria as well.
9
We can now construct a simple example that applies Proposition 4.1 above without explicitly computing the second-best solution. We slightly alter the example of the previous
134
BENHABIB AND RUSTICHINI
section by adding a constant to the production function: y -first-best consumption policy is
ak + b.
= Min(~y -I- ~,
In this case the
y/2),
(13)
where 7
= ~.b/(a -
1) _> O.
For any L and 0 =
Lb/(a -
v(k) = s (ak +
(14)
1), the first-best value function is
a -b 1 )
~-~ '
(15)
where s is given by (7) as before.
The optimal defection policy against a player consuming c --- )~y + O is
CD(k'~'Y+O)=min(M((1-)~)Y+(
where
c < y/2 and 0 = ~.b/(a -
a-la
~')(a-~))'(1-)~)Y-O)
'
(16)
1). The defection value is then given by
vD(k, (1-- ;.)y + o) = sD [y + (((a ll)~-/~) - L) (b/(a -1))]l-~
where SD is defined in (9).
We now assign parameter values to the example above as follows: a = 1.058, b = 0.025,
fl = .95, e = .2. With these values, for k > 1.2 we have ~3(k) > v~
6(k)), while for
~(k)). It is easily shown that for k > 0.02 the first-best strategies
k < 1.1, fi(k) < v~
lead to growth at the rate of about 2.5 percent. Thus for k > 1.2, this growth rate can be
sustained as a first-best equilibrium. However, for k in [0.4, 0.9], conditions of the above
proposition apply. For k = 0.4 ( = 0.9) ~ defined in the proposition is given by 0.10015
(0.05055) and y - 2? - k < 0. Therefore even the second-best equilibrium cannot generate
growth for k 6 [0.4, 0.9]. We can check that for k > 0.4 we have y - 2~(k) > 0 and
y - ~(k) - cD(k) > O.
The above example and proposition allow us to starkly establish how growth rates can
depend on wealth because incentive constraints can be strongly binding at some wealth levels
and weakly binding at others. In fact, in our example incentive constraints are not binding
at all for k > 1.2, but they are binding and prevent positive growth for k c [0.4, 0.9]. The
empirically more relevant issue however arises in the region k 6 [0.9, 1.2] where growth is
possible along the second best but at rates lower than the first-best constraints. In the next
section we provide an explicit example to illustrate this.
SOCIAL CONFLICT AND GROWTH
5.
135
Slow-Growth Equilibria and Growth Traps
In the next example we derive explicitly a second-best policy for which growth toward a
high steady state occurs from large stocks but not from low stocks. First-best policies that
are not incentive compatible always lead to the unique steady state with positive stocks, but
second-best policies may not. The value function for this example is discontinuous even
though technology and preferences are convex and continuous. As in the previous section,
the players have identical preferences and are equally weighted.
As mentioned in the introduction, the case of slow growth at low wealth levels is more
likely to obtain when marginal utility is low at high wealth levels and when the marginal
product of capital is not too high at low levels of capital--as, for example, in the case of
technologies that are linear in capital. Under diminishing marginal utility, deviation at high
wealth levels with a large chunk of consumption is less appealing. At the same time, if
the marginal product of capital is not too high at low wealth levels, the benefits of fast
accumulation can be more easily sacrificed, especially if consumption is low and marginal
utility is sufficiently high to make defection more attractive. The example below illustrates
these points.
We consider the production function
f(k)=
Ak
A + B(k-1)
k<_l
k>l,
B / 2 < 18
(18)
with A = 5/2 and 13 = 1/2. The utility function is
U(c)
/ c
ifc < 1
I l+b(c-1)
if c > 1.
Since A/3 > 1 > Bfl, k = 1 is a steady-state stock for the optimal growth problem with
c = 3/4 as the steady-state consumption. We assume b is small:
A/~
B fl < b < -~ < 1 .
We spare the reader a detailed discussion of the details of the example. For a complete treatment we refer to Benhabib and Rustichini (1991, sec. 4.2 and app. A.2.1). The conclusions
of the example are clear from Figures 2a and 2b.
There are five values of the capital stock that mark the extreme points of intervals over
which the second-best value and the consumption policy have different behavior. 9 ko = 1
is the first-best and second-best steady state with positive stocks. The value function is
piecewise linear. Two points are noteworthy. First, the value is convex on the interval
[0, k3) and concave in [k3, +c~). Second, the value function is discontinuous (but uppersemicontinuous) at k3. We emphasize again that both the production and utility functions
are concave (so that the first-best value function is necessarily concave and continuous).
For k _> kl the second-best value (and the consumption policy) are the same as the first
best. For lower values, the consumption level for second best has to be higher to satisfy
13 6
BENHABIBAND RUSTICHINI
,bj
0
k4 k3 k2 kl
(a)
%b
\
k4
k3 k 2
/
k1
(b)
Figure 2.
the equilibrium conditions; growth is slower, and the second-best value is strictly below the
first best. More precisely, for k e [k3, kl ] the second-best policy prescribes the minimum
consumption that makes the second-best value equal to the value of defection. Consumption
is decreasing over the range where the incentive compatibility constraint is binding and
then increasing when the second-best solution is the first best. Overall, the second-best
consumption is nonmonotonic, even in the region where we have steady growth. Note that
over [k3, k]) the first-best consumption is lower than the second best. As k increases, the
incentive constraint becomes less binding, and second-best consumption decreases with
k along the equilibrium. The intermediate region ([ka, kl]) has the lowest consumption
137
SOCIAL CONFLICT AND GROWTH
above k4. Finally, the consumption policy is continuous except at k3. The reason for
the discontinuity of the consumption policy and the value function may be understood as
follows. As k decreases, progressively higher levels of consumption are needed in order to
make the value of second best, and the value of defecting from it, equal to each other. To
higher levels of consumption corresponds a reduction in both the continuation value and the
postdefection value. The rate at which these two second-period values change is different.
The rate of the defection value is constant while the rate of the second-best continuation
value is changing with k because the second-best value is concave. When the difference
between these two rates changes sign and becomes negative, no increase in consumption
can equate the second best and the value of defection and at the same time allow the
capital stock not to decline. (Computations underlying this example are in Benhabib and
Rustichini, 1991.)
The dynamics of the capital stock in the second-best solution gives even more dramatic
evidence of the discontinuity at k3. For k ~ [k3, kl ], the capital stock grows toward the
same steady state as the first best but more slowly: we denote this region as one of "slow
growth." For k < k3, we have a "growth trap": the capital stock contracts to zero, which is
a stable steady state for the dynamics of the second best. The region of wealth for which
we have "slow growth," the interval (k3, kl), is probably of greater empirical interest. Here
the growth rate is lower than the first best. Only after the threshold wealth level of kl has
been reached does growth resume its higher first-best level. 1~
6.
An "Olson" Case
In the previous sections we showed how incentive constraints could result in equilibria for
which growth occurs from high stocks but not from low stocks. In the following example the
opposite is true. In contrast with the previous examples, the utility function is linear, but the
production function is Cobb-Douglas. The linear utility makes it attractive to defect from
high stocks with a large consumption. On the other hand, with a Cobb-Douglas technology,
when stocks are low, their marginal product is high and defection is unattractive. Therefore
at low stocks players follow first-best policies to accumulate the precious capital. As stocks
get larger, defection becomes more attractive, and accumulation has to slow down. Firstbest policies are abandoned, and the economy stops short of the first-best steady state. In
the spirit of the work of Mancur Olson (1982) inefficiency emerges at high rather than low
levels of wealth.
Let the production functionbe f ( k ) = k% a e (0, 1), and the utility functionbe U ( c ) = c.
The optimal solution has a steady state given by
k* = (o~fl)~-~'~.
(19)
The optimal policy is, as usual,
~(k)=
.1
;
0
if k < k
E_~
if k > k * ~ ,
(20)
138
BENHABIB AND RUSTICHINI
and the first-best value of the steady state is
~(k*)
=
-
-
1-/3
Consider now a given level of capital stock k and consumption c for one of the players.
Then the value of defection for the other player is
vD (k, C) ~- maxc' + ~ ( k ~ - c - c') '~.
c' >0
(21)
The optimal defection consumption is clearly in the interval [0, k" - c):
0
CD(k,c)=
with y
=
ka - c - y
2
if (k ~ - c) "-1 > -7'
(22)
otherwise
(Ogfl/2) l/1-~ The associated value function for defection is
vD(k,c) =
2
"~(k~--c)" i f ( k ~ - c ) ~-1 > g~,
k" - c + ( otherwise
(23)
where ( = V~'(/3/2) - y. Note that if the net stock left by the other player, k" - c, is too
low, then the optimal defection policy is to consume nothing.
Before we proceed, we define the set of incentive compatible steady states; in this example
these are values of k such that the following inequality holds:
f(k)-k
oD ( f ( k ) - - k )
-~-~-_-~-~ >
k,
2
"
(24)
These are therefore the values ofk such that the value for each player of keeping k as a steady
state is larger than the value of defecting from this pair of capital stock and consumption.
This set will be useful in determining the second-best value and policy. For any value of
or, 13 the inequality above is equivalent to/3k ~ - (2 - / 3 ) k - 2((1 - / 3 ) _> 0, so the set of
values of k that satisfy the above inequality is a (possibly empty) interval, k < k < k. Note
that for the proposition below, the lowest k from which f< may be reached in one step by
consuming nothing is given by f0/'L A proof is in Benhabib and Rustichini (1991).
P r o p o s i t i o n 6.1: On the interval [max{k, f~l/~), ~] we have (1) if k* < fc, the first-best and
second-best value functions and consumption policies coincide: Vsb(k) = ~ (k), Csb(k) =
6 (k ) ; (2) if f< < k*, that is the first-best steady state is above the range of incentive compatible
sustainable steady states, then the second-best values are Vsb(k) -----(k ~ q- k)/2 + (, and
Csb(k ) = (k ~ - [c/2; (3) ilk < lc1/~, the second-best value strictly dominates defection--that
is, Vsb(IcUa) > vD (lc1/~, Csb(lcl/a) ). Furthermore for an interval [kl, ~l/a] we have
vsb(k) = / 3 k'~2 + f: + / 3 ( ,
2
~(k) = Csb(k) = O,
SOCIAL CONFLICT AND GROWTH
139
that is, the first- and second-best consumption policies coincide, but the value functions do
not.
It is easy to show that both the case fr < k* and the case k* < fr are possible. For
example, for (or,/3) = (.975, .97), case 2 in Proposition 7.1 occurs with k* = .1074,
fr = .0906. However, when (or, 13) = (.9142, .92), then k* = .1329, fr = .1542. It is
also easy to see that, for different values of t~, both cases may occur for any given value of
the discount factor. In the case where k < k*, we know that the second-best policy over
[fr
~] is to consume as much as needed to go to t: in one step. However, on [kl, fr
the second-best consumption is the same as the first-best consumption, which is zero. The
second-best accumulation path then stops at k, while the first best grows to k*. For higher k,
second-best consumption is higher than the first best. Therefore on [kl, fcl/a], when stocks
are low, players follow first-best strategies but stop doing so above ~l/a. (Note also that
l)sb(fgl/a) __ l)O (~l/t~, Csb(~l/a)) > 0 for the (or, fl) pairs given above; this implies k < fcl/a.)
7.
Final Remarks
Some empirical evidence suggests that poor countries fail to grow at rates suggested by
standard economic models because their saving and investment rates are low. We provide a
political economy model of interest groups in which returns to investment are appropriable
by other groups. This framework transforms the accumulation problem into a commons
problem that may lead to underinvestment equilibria. Our contribution is to focus on
second-best subgame perfect equilibria to show that growth rates can indeed be wealth
dependent. Poor countries may indeed accumulate at lower rates because even for the best
sustainable equilibria, the incentives for appropriation can be much stronger at low levels
of wealth than at high ones, and therefore the momentary advantages of defection can be
overcome only with high consumption and low investment rates. This, of course, is not
the only explanation for why poor countries save little, but it is a plausible one. We also
show through examples that second-best equilibria can result in low growth at high rather
than low wealth levels, and we refer to such situations as "Olson" cases, after the work
of Mancur Olson. With some work it should be possible to come up with examples of
second-best equilibria that combine the two polar cases and generate a u-shaped relation
between growth rates and the level of wealth.
Acknowledgments
We would like to thank V. V. Chari, Douglas Gale, Boyan Jovanovic, Ehud Kalai, Pat Kehoe,
Roy Radner, and Chuck Wilson and anonymous referees for very helpful comments. We also
would like to thank the C. V. Starr Center for Applied Economics at New York University
for technical assistance.
BENHABIB AND RUSTICHINI
140
No~s
1. On this empirical regularity there is wide agreement, see De Long (1988), Baumol and Wolff (1988, fig. 2),
and Easterly (1991).
2. Some of tbe nonviolent redistributive mechanisms that are used in developing countries include nationalization;
bursts of inflationary finance to sustain the incomes of government bureaucracies and the military; the squeezing
of the agricultural sectors in favor of politically powerful urban coalitions through exchange rate policies, price
controls, and monopolistic marketing boards; legislation and other measures that alter the bargaining power
of labor (either positively or negatively); the allocation of highly desirable government and civil service jobs
and university admissions to favored ethnic and tribal groups; and large-scale bureaucratic corruption tolerated
and condoned by the government.
3. For specific and detailed discussions in particular cases, see O'Donnell (1988) or Olson (1982).
4. As pointed out by a referee, such institutional arrangements may be easier to implement at higher income and
wealth levels and account for lower growth rates of poor countries.
5. While we adopted a symmetric specification for the allocation rule, this can easily be modified. To assign
asymmetric appropriation power to the players we could have assumed that one of the players can obtain up
to, say, three-fourths of the output under fast consumption strategies (?1, ~2), and confine the consumption of
the opposing player to one-fourth of the output. What sustains fast consumption as an equilibrium is that any
attempt to save by a player is defeated because the opposing player then exhausts the residual. Positive savings
may be possible if the fast consumption rates of one or both players are bounded--that is, if f ( k ) - ~j > 0
where ?j is the bound for the consumption rate of the j t h player. Conditions under which fast consumption
rates are still equilibrium strategies when positive savings rates are possible have been studied (in a continuous
time framework) by Benhabib and Radner (1992) for the case of linear utility and by Rustichini (1992) with
nonlinear utility.
6. Note that a standard contraction mapping argument to ensure that the continuity of the value function cannot
be used. Section 5 provides an example of a discontinuous value function. In general, standard conditions to
apply dynamic programming methods and the contraction mapping, which ensure the continuity of the value
function, may not hold for our problem. Blackwell's discounting condition T ( v + or) < T ( v ) § flt~ can be
violated because the constraint set for v + c~ becomes larger, allowing consumption levels that would be ruled
out under v.
7. A sufficient interiority condition for ~ = ~.y + ~ <_ y / 2 for all k > 0 is computed to be fla _> 1. This condition
will be satisfied in all examples below.
8. Note that the utility and production functions are made piecewise linear for computational convenience. They
may be approximated with nonlinear functions that smooth the corners to generate an example of switching
with nonlinear preferences and technology. It would be interesting to resolve the question of whether given an
arbitrary concave production function, it is possible to construct a utility function that generates a switching
equilibrium.
9. The ki's in Figures 2a and 2b are k0 = 1, kl = 14/15, k2 = 68/75, k3 = 1018/1125, k4 = 4/5, k5 = 0. Let
the value function be Vsb = ai k q- bi and the consumptions be given by Csb = m i k -1- hi. The values ai, bi,
mi, rli hold over the interval [ki+l, ki], and are given by
ao =
5
25
175
25
5
~ , a l = T g , a 2 = - s T , a 3 = 7g,,,4 = ~;
1
1
43
bo ---- ~ , b l = - ~ , b 2 = - ' - ~ , b 3 = - ' ~ , b 4 = O ;
mo=
1
5
25
5
~ , m l = O ; m 2 = --~--;m3 = O ; m 4 = ~;
1
no ----- - ~ ; n l
2
19
= ~ ; n 2 = "~-;n3 = 1;n4 = 0 .
SOCIAL CONFLICT AND GROWTH
141
10. Countries like Korea and Chile, among others, provide possible examples of a switch from low to high growth
rates in the recent past. In both cases suppression of interest groups under authoritarian regimes may have
increased the cost of defection and appropriation, making way for first-best growth. Later, once the original
switching threshold was crossed, first-best growth may have become self-sustaining and the authoritarian
regimes toppled, as they no longer were necessary to sustain growth. A more recent example, following the
path of Chile, may be Peru. Also, for an exposition of the role of group conflict in retarding growth in Argentina
prior to the recent acceleration in growth rates, see MaUon and Sourrille (1975) and O'Donnell (1988).
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