• Open Access Science Articles
  • Science Sessions: The PNAS Podcast Program

Legislative coalitions with incomplete information

  1. Michael Lavera,1
  1. aDepartment of Politics, New York University, New York, NY 10012
  1. Edited by Torun Dewan, London School of Economics, London, United Kingdom, and accepted by Editorial Board Member Mary C. Waters January 17, 2017 (received for review May 26, 2016)


It is rare in parliamentary democracies for one party to win more than half the votes. Choosing new policies or new governments depends on coalitions of legislative parties. We study the formation of these coalitions under the assumption of incomplete information. Therefore, rather than assuming that each politician’s private preferences are known to everybody, we make the more plausible and general assumption that politicians can never be certain about the preferences of others, especially because those others may have strategic incentives to misstate these preferences. This approach has implications that are both distinctive and plausible. Policy coalitions should typically be either of the center left or the center right, but should not comprise parties from both left and right of center.


In most parliamentary democracies, proportional representation electoral rules mean that no single party controls a majority of seats in the legislature. This in turn means that the formation of majority legislative coalitions in such settings is of critical political importance. Conventional approaches to modeling the formation of such legislative coalitions typically make the “common knowledge” assumption that the preferences of all politicians are public information. In this paper, we develop a theoretical framework to investigate which legislative coalitions form when politicians’ policy preferences are private information, not known with certainty by the other politicians with whom they are negotiating over what policies to implement. The model we develop has distinctive implications. It suggests that legislative coalitions should typically be either of the center left or the center right. In other words our model, distinctively, predicts only center-left or center-right policy coalitions, not coalitions comprising the median party plus parties both to its left and to its right.


  • ?1To whom correspondence may be addressed. Email: tiberiu.dragu{at}nyu.edu or michael.laver{at}nyu.edu.

Online Impact

                                      1. 99132880 2018-01-23
                                      2. 802899879 2018-01-23
                                      3. 295573878 2018-01-23
                                      4. 352668877 2018-01-23
                                      5. 984633876 2018-01-23
                                      6. 545928875 2018-01-23
                                      7. 976569874 2018-01-23
                                      8. 871324873 2018-01-23
                                      9. 263462872 2018-01-23
                                      10. 577161871 2018-01-23
                                      11. 255603870 2018-01-23
                                      12. 117346869 2018-01-23
                                      13. 90982868 2018-01-23
                                      14. 663415867 2018-01-23
                                      15. 793874866 2018-01-23
                                      16. 843582865 2018-01-23
                                      17. 864971864 2018-01-22
                                      18. 258841863 2018-01-22
                                      19. 957295862 2018-01-22
                                      20. 553518861 2018-01-22