Revised 04/06/05 Mixed-Member Proportional Electoral Systems in New Democracies: The Bolivian Experience by Miguel Centellas Department of Political Science 3438 Friedmann Hall Western Michigan University Kalamazoo, MI 49008 miguel.centellas@wmich.edu This paper considers the effects of the change in Bolivia’s electoral system from list proportional (list-PR) to mixed-member proportional (MMP). One of the most noticeable effects of the 1994 change was increased regionalization and party system fragmentation. Prior to the change, Bolivi- an politics revolved around a stable, moderate multiparty system organized around two blocks (MNR and ADN-MIR). In the two elections following the change to MMP, the country’s electoral system has fragmented, clustering around regionally entrenched, antagonistic parties. Using statis- tical analysis of disaggregate electoral data from the country’s five elections (three prior to MMP, two after MMP), this paper argues that the change to MMP increased the importance of regional cleavages, and argues that this was a contributing factor to the dramatic overthrow of then- president Gonzalo Sanchez de Lozada in October 2003. Such a finding gives reason to question the recent popularity of MMP by the discipline’s electoral engineers. While regional differences existed throughout Bolivia’s democratic experience, these were strengthened and polarized after the change to MMP. Prepared for delivery at the 63rd Annual Meeting of the Midwest Political Science Asso- ciation, Chicago, 6-10 April 2005. I thank Kevin Corder for his comments and advice. Available online at: http://www.centellas.org/politics/papers/mpsa2005.pdf