Social Choice and Welfare

, Volume 11, Issue 4, pp 355–380 | Cite as

A theory of policy differentiation in single issue electoral politics

  • John E. Roemer


Voter preferences are characterized by a parameter s (say, income) distributed on a set S according to a probability measure F. There is a single issue (say, a tax rate) whose level, b, is to be politically decided. There are two parties, each of which is a perfect agent of some constituency of voters, voters with a given value of s. An equilibrium of the electoral game is a pair of policies, b1 and b2, proposed by the two parties, such that b i maximizes the expected utility of the voters whom party i represents, given the policy proposed by the opposition. Under reasonable assumptions, the unique electoral equilibrium consists in both parties proposing the favorite policy of the median voter. What theory can explain why, historically, we observe electoral equilibria where the ‘right’ and ‘left’ parties propose different policies? Uncertainty concerning the distribution of voters is introduced. Let {F(t)}t ε T be a class of probability measures on S; all voters and parties share a common prior that the distribution of t is described by a probability measure H on T. If H has finite support, there is in general no electoral equilibrium. However, if H is continuous, then electoral equilibrium generally exists, and in equilibrium the parties propose different policies. Convergence of equilibrium to median voter politics is proved as uncertainty about the distribution of voter traits becomes small.


Probability Measure Reasonable Assumption Median Voter Policy Differentiation Single Issue 
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  1. Alesina A (1988) Credibility and policy convergence in a two-party system with rational voters. Am Econ Rev 78: 796–805Google Scholar
  2. Alesina A, Roubini N (1990) Political cycles in OECD economies. NBER Discussion Paper no. 470Google Scholar
  3. Calvert RL (1985) Robustness of the multidimensional voting model: candidate motivations, uncertainty, and convergence. Am J Polit Sci 29: 69–95Google Scholar
  4. Calvert RL (1986) Models of imperfect information in politics. Chur Harwood Academic PublishersGoogle Scholar
  5. Hansson I, Stuart C (1984) Voting competitions with interested politicians: platforms do not converge to the preferences of the median voter. Publ Choice 44: 431–441Google Scholar
  6. Palfrey T (1984) Spatial equilibrium with entry. Rev Econ Stud 51: 139–156Google Scholar
  7. Persson T, Tabellini G (1990) Is inequality harmful for growth? Institute for Internatioal Economic Studies, University of California, BerkeleyGoogle Scholar
  8. Przeworski A, Sprague J (1986) Paper stones. University of Chicago Press, ChicagoGoogle Scholar
  9. Roemer JE (1994) On the relationship between economic development and political democracy. Econ Design (in press a)Google Scholar
  10. Roemer JE (1994) The strategic role of party ideology when voters are uncertain about how the economy works. Am Polit Sci Rev (in press b)Google Scholar
  11. Roemer JE (1993) Political-economic equilibrium when parties represent constituents: the unidimensional case, Department of Economics, University of California, Davis, Working Paper No. 93–19Google Scholar
  12. Wittman D (1983) Candidate motivation: a synthesis of alternative theories. Am Polit Sci Rev 77: 142–157PubMedGoogle Scholar
  13. Wittman D (1990) Spatial strategies when candidates have policy preferences. In: Enelow J, Hinich M (eds) Advances in the spatial theory of voting. Cambridge University Press, CambridgeGoogle Scholar

Copyright information

© Springer-Verlag 1994

Authors and Affiliations

  • John E. Roemer
    • 1
  1. 1.Department of EconomicsUniversity of CaliforniaDavisUSA

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