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Manuscript prepared for publication in
Studies in Microeconomics
May 2014
Transferable Utility in the Case of Many Private and Many Public Goods
Elisabeth Gugl1
Abstract
It is possible to have income effects on more than one good in utility profiles that lead to Transferable Utility and in the presence of many private and many public goods. Assuming that the utility functions are of the Generalized Quasi-‐linear form is not necessary for TU to hold. I present a much broader class of utility profiles generating TU in which GQL emerges as a special case.
1 Department of Economics, University of Victoria, P.O. Box 1700 STN CSC, Victoria, BC, V8W 2Y2, Canada. Email: [email protected] I would like to thank Ted Bergstrom, Pierre-‐André Chiappori, Somdeb Lahiri, an anonymous referee, and Linda Welling for their helpful comments.
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1. Introduction
Chiappori (2010) derives testable implications of Transferable Utility (TU) by stating conditions on demand that have to be satisfied. One condition is that there can be only one private good which has a strictly positive income effect. This condition relies on the assumption that TU requires utility functions of the Generalized Quasi-‐linear (GQL) form. In this article I point out that while TU is satisfied if utility functions are of GQL form, there are other utility functions for which TU is satisfied and they do allow for strictly positive income effects on more than one private good. In fact, Bergstrom has made this argument repeatedly Bergstrom (1989, 1999) and it goes back to Bergstrom and Varian (1985). This article therefore accomplishes two goals. To recall the exhaustive list of indirect utility functions that lead to TU in the presence of private and public goods and to give examples of a broader range of utility functions satisfying TU than the subclass considered by Chiappori.
Chiappori identifies testable implications of an important subclass of utility functions that lead to TU, but they are by no means necessary for TU to hold. Hence Chiappori's results in his 2010 article should be read as testable implications of GQL utility functions, rather than TU itself.
In the next section I introduce the model following Chiappori's notation as much as possible. I give examples of utility profiles satisfying TU with and without the consideration of public goods. Then I present a broad class of utility profiles satisfying TU when many private and public goods are considered. As noted this class is considerably larger than utility profiles generated by GQL utility functions.
2. The Model
Consider a group of
�
S individuals with preferences over
�
L private goods and over
�
N public goods. The public goods are public within the group only. The group purchases these goods in the market at prices
�
p,P( ) where
�
p = p1,..., pL( ) is the price vector for private goods and
�
P = P1,...,PN( ) is the price vector for public goods. Each individual
�
m ∈S consumes a commodity vector
�
xm ,X( ) where
�
xm = xm1 ,...,xm
L( ) is the vector of private goods consumption and
�
X = X1,...,XN( ) is the vector of public goods consumption. Each individual has a fixed income of
�
ym and the group's income is given by
�
y = ym∑ . The group's budget constraint is given by
�
pxm + PX = ym∈S∑ (1)
Denote by
�
um xm,X( ) the utility function of group member
�
m . In what follows it will be useful to distinguish between the group expenditure on public goods and
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individual expenditure on private goods. For any fixed
�
X , the disposable income of group
�
S for private consumption goods (in short disposable income) is
�
I = y − PX .
Denote by
�
Im individual the disposable income of member
�
m , such that
�
Im = I∑ .
The indirect utility function conditional on given amounts of the public goods is given by
�
vm X, p,Im( ) . It is the value function of the maximization problem
�
maxxm u xm,X( ) s. t. pxm = Im
We next recall the definition of TU following Chiappori (2010).
Definition 1 The framework defined above satisfies the transferable utility (TU) property on some open set
�
Ο of price-‐income bundles if the following property is satisfied: for each agent
�
m , there exists a cardinal representation
�
um of
�
m ′s utility such that for each
�
p,P,y( ) ∈Ο there exists a
�
λ ∈ℜ such that the utility possibility frontier defined by the budget constraint (1) is the hyperplane defined by
�
um = λm∈S∑ . Because
�
λ ∈ℜ depends on
�
p,P,y( ) and on the utility profile
�
u , we denote it by
�
λ p,P,y,u( ) .
3. Results
The discrepancy between Bergstrom's and Chiappori's interpretation of what is required for TU seems to stem from a fundamental disagreement of what is required for TU in exchange economies with private goods and convex preferences. Chiappori (2010, p. 1305) notes, "When all commodities are privately consumed, then TU is known to be equivalent to quasi-‐linear utilities, which requires zero income elasticity for all demands but one." Contrary to this claim, Bergstrom and Varian (1985) established that in an exchange economy with private goods only, the indirect utility functions of any individual
�
m ∈S must be of the Gorman polar form for there to be TU.2
Proposition 1 Bergstrom and Varian (1985). With
�
L ≥ 2 and
�
N = 0 , there is TU if and only if
�
vm p,Im( ) = α(p)Im + βm (p) (2)
where
�
α(p) and
�
βm (p) are functions of the price vector only.
Proof of Proposition 1 To see these indirect utility functions yield TU, note that without public goods, the UPF gives us all the combinations of agents' utilities that
2 Bergstrom and Varian (1985) prove their result while Chiappori's statement is based on his reading of the literature.
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arise from different distributions of
�
I . It follows that if individuals' indirect utility functions are of the Gorman form, then the sums resulting from different distributions of
�
I are the same
�
vm p,Im( ) = α(p)I +m∈S∑ βm (p)m∈S∑
A change in the distribution of
�
I has therefore no impact on the sum of indirect utilities and hence the UPF for each
�
(p,y)∈Ο is given by
�
um = α(p)I +m∈S∑ βm (p)m∈S∑
Transferable utility holds. QED.
Bergstrom (1999, p.19), interpreting the Bergstrom-‐Varian result, points out, "The Gorman class includes preferences represented by a quasi-‐linear direct utility function. [...] But the Gorman class also includes identical homothetic preferences and more generally, preferences which, like the Stone-‐Geary utility function, are represented by utility functions of the form
�
[U(xm − em )] , where U is a homogenous function and
�
[em ] is some vector that "displaces the origin" and which may be different for different people. Thus it is possible to have transferable utility, but to have preferences differing among individuals and to have income-‐responsive demand for all goods."3
Example 1 Consider two people
�
m = 1,2 with their utility functions given by
�
um xm( ) = xm1( )a xm2( )1−a + xm
3( )bm where
�
0 < a,b1,b2 < 1. The indirect utility functions are then of the form given by (2) with4
�
α(p1, p2) =ap1
⎛ ⎝ ⎜
⎞ ⎠ ⎟ a 1− a
p2⎛ ⎝ ⎜
⎞ ⎠ ⎟ 1−a
β(p1, p2, p3) = p3α(p)( )bmbm −1
1bm
−1⎛ ⎝ ⎜
⎞ ⎠ ⎟ 1bm
⎛ ⎝ ⎜
⎞ ⎠ ⎟
1bm −1
From the indirect utility function above, it is clear that goods 1 and 2 have an income effect while good 3 has not.5 This means that this example already shows
3 Notation changed for consistency with remainder of the article. 4 It is clear that corner solutions are possible. It should be noted that corner solutions also occur with quasi-‐linear utility functions alone and hence moving to other forms of utility functions does not restrict the range in which TU holds any more than by choosing a particular quasi-‐linear specification. These non-‐negativity constraints are largely ignored in the literature. As this article is mostly a comment on the existing literature I do not focus on corner solutions either.
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that it is possible to generate TU and observe demands for more than one good that change with income.
Incorporating public goods into the model leads to specific requirements of how they need to enter utility functions in order to preserve TU. For example, if all agents have identical and linearly homogeneous CES utility functions in the case of all private goods, we have TU, but making one of the goods a public good does no longer lead to TU.
Example 2 Assume there are two individuals and they have utility functions of the form
�
um X,xm1 ,xm
2( ) = X a + xm1( )a + xm
2( )a( )1a
where
�
0 < a < 1.
Given
�
X , the indirect utility function for each individual is given by
�
vm p,Im ,X( ) = X a + α(p)Ima( )1a
Given
�
X , we would need to distribute income
�
I in different ways to pick up all the different distributions on the UPF. But note, the UPF will no longer be of TU form, because the sum of indirect utilities changes with different distributions of
�
I . Letting
�
X vary, could we still get TU? The answer is no. To examine the properties of the UPF, we can use the indirect utility functions derived above. Let
�
µ, φ be Lagrange multipliers, we need
�
maxX ,I1 ,µ,φ X a + α(p)Ima( )
1a + µ X a + α(p)(I − Im )
a( )1a − u2
⎛ ⎝ ⎜
⎞ ⎠ ⎟ + φ(y − PX − I)
This leads to the Samuelson Condition of efficient provision of public goods
�
X a−1
α(p)I1a−1 +
X a−1
α(p)(y − PX − I1 )a−1 = P
The Samuelson Condition tells us that the efficient amount of the public good is not independent of the distribution of disposable income. Bergstrom and Cornes (1983) proof that the efficient amount of the public good must be independent of the distribution of disposable income for TU to hold and hence the utility profile in Example 2 does not lead to TU.
5 By Roy's identity, the demand of a good
�
xml is given by
�
xml p,Im( ) = −
∂vm /∂pl
∂vm /∂Im. Since the
demands for goods
�
l = 1,2 depend on
�
Im , they have an income effect.
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Bergstrom and Cornes (1983) show that in order to lead to TU, utility functions with one private good and many public goods must be of the type
�
um xm,X( ) = b(X)xm1 + Am (X) (3)
Chiappori considers many private goods in addition to many public goods and makes the following generalization to (3).
Definition 2 A utility function is of the Generalized Quasi-‐linear form if the function can be written as
�
um xm,X( ) = b(X)xm1 + Am (xm
2 ,...,xmL ,X)
Chiappori (2010) then shows that if
�
bm (X) is the same for all agents, TU holds. 6
Taking a different approach, Bergstrom (1999) focuses again as in Berstrom and Varian (1985) on indirect utility functions and notes that agents' indirect utility functions must be of the form
�
vm X, p,Im( ) = α(p,X)Im + βm (p,X) (4)
for TU to be satisfied in the case of many private and many public goods.7 That these indirect utility functions lead to TU can be easily seen by considering the Samuelson Condition again. Given (4), the condition for the efficient amount of any public good
�
X n is given by
�
∂α∂Xn Im +
∂βm
∂Xn
α(p,X)m∈S∑ = Pn or equivalently
�
∂α∂Xn I +
∂βm
∂Xnm∈S∑α(p,X)
= Pn
This means that the efficient amount of any public good is independent of the distribution of
�
I . It implies that in order to solve for the UPF, one can solve the following problem
6 Chiappori makes the following statements on page 1305: "Necessary and sufficient conditions for transferability have been known for some time. [...] In a seminal contribution, [Bergstrom and Cornes (1983) and Bergstrom (1989)] have shown that transferable utility (TU) requires three properties:
1. individual utilities are of the generalized quasi-‐linear form with respect to the same commodity, say 1; 2. the
�
bm (X) functions are identical across agents:
�
b1(X) = ...= bS (X) = b(X) ; 3. the allocation of resources between members is such that each member has a positive consumption of commodity 1."
Note that Bergstrom himself does not claim that the case of many private goods and many public goods is considered in Bergstrom (1989) or Bergstrom and Cornes (1983) as Chiappori seems to state in above quote. 7 Bergstrom (1999) does not formally prove this statement or provides a reference to a formal proof but claims that the result is obvious by combining the Bergstrom-‐Varian (many private goods) and the Bergstrom-‐Cornes (many public goods, one private good) results.
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�
λ(p,P,y,u) = maxX ,I ,φ α(p,X)I + βm (p,X)m∈S∑ + φ(y − PX − I)
and the UPF is then given by
�
um = λm∈S∑ (p,P,y,u)
We now ask the question which utility functions would lead to such indirect utility functions. It is straightforward to verify that utility functions of the GQL form with identical
�
bm (X) functions lead to indirect utility functions given by (4). However, GQL is not necessary for TU in case of many private and many public goods just as quasi-‐linear utility functions are not necessary in the case of all private goods. Below I present a much larger class of utility functions that lead to TU.
Proposition 2 Partition the set of private goods into
�
L1 and
�
L2 such that
�
∅ ≠ L1 ⊆ L and
�
L2 ⊂ L . Then any utility functions of the form
�
um xm,X( ) = A(X)h xmk{ }k∈L1
− em( ) + Bm X, xml{ }l∈L2( ) (5)
where
�
h xmk{ }k∈L1( ) is homogenous of degree 1 and
�
em is some vector of fixed
quantities, will lead to TU.
Proof of Proposition 2 To proof Proposition 2, note first as in the Example 1, that the demand for any private good
�
l ∈L2 depends on the whole price vector but not on disposable income. Once these demands are found -‐-‐ we denote them by
�
xml (p,X) -‐-‐
we can write the utility maximization problem as
�
max{xmk }k∈L1 A(X)h {xmk }k∈L1 − em( )
s. t. {pk}k∈L1 {xmk }k∈L1 = Im − {p
l}l∈L2 {xml }l∈L2
Since this problem is just like solving for an indirect utility function with a utility function that is of the Stone-‐Geary form, the indirect utility function for this problem -‐-‐ denoted by
�
ϖm X, p,Im( ) -‐-‐ is given by
�
ϖm X, p,Im( ) = γ X,{pk}k∈L1( ) Im − {pl}l∈L2 {xml (X, p)}l∈L2( ) Assembling all the partial results, we end up with an indirect utility function of (5) given by
�
vm X, p,Im( ) = γ X,{pk}k∈L1( )Im − γ X,{pk}k∈L1( ){pl}l∈L2 {xml (X, p)}l∈L2 + Bm X,{xml (X, p)}l∈L2( )
This indirect utility function is of the desired form (4) with
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�
α X, p( ) = γ X,{pk}k∈L1( ) and
�
βm X, p( ) = Bm X,{xml (X, p)}l∈L2( ) − γ X,{pk}k∈L1( ){pl}l∈L2 {xml (X, p)}l∈L2
I conclude this section by pointing out special cases of (5). Chiappori's GQL emerges as the special case with L₁=1. Another special case is the Generalized Cobb-‐Douglas (GCD) utility function given by
�
um xm,X( ) = A(X) xm1( )γ 1 × ...× xm
L( )γ L + Bm (X)
where
�
γ k = 1k∈L∑ . Yet, another example is a hybrid of the GCD and GQL forms given
by
�
um xm,X( ) = A(X) xm1( )γ 1 × ...× xm
L1( )γ L1 + Bm (X,{xml }l∈L2 )
where
�
γ k = 1k∈L1∑ .
4. Conclusion
In many theoretical models in which TU is invoked, there is only one private good and one public good, so the Bergstrom-‐Cornes result applies which can be considered as a special case of the GQL form with
�
L = 1 and hence the discussion in this article is irrelevant. However, if the focus is on empirical implications of TU acknowledging that families or other groups of people consume many private and public goods, then focusing on GQL is too narrow. As I have shown here, utility functions outside the class of GQL also satisfy TU. While any of the examples given make strong assumptions about people's preferences, they do admit for more than one private good having a positive income effect. Developing tests for the larger class of utility functions is left to future research.
References
Bergstrom, Th. C., 1989, A Fresh Look at the Rotten Kid Theorem -‐-‐ and Other Household Mysteries, Journal of Political Economy 97, 1138-‐59.
Bergstrom, Th. C., 1999, A Survey of Theories of the Family in Handbook of Population and Family Economics. Edited by M.R. Rosenzweig and O. Stark, volume 1A, 22-‐79.
Bergstrom, Th. C. and R. C. Cornes, 1983, Independence of Allocative Efficiency from Distribution in the Theory of Public Goods, Econometrica 51, 1753-‐66.