Strategic Voting under Plurality and Runoff Rules

Choosing a method of electing a president is often a contentious constitutional issue for newly emerging democracies. The debate focuses largely on two alternative electoral procedures: plurality rule and plurality rule with a runoff. Duverger (1954) argues that plurality rule has a consolidating influence on parties that a runoff rule lacks. This paper focuses on the `psychological effect' identified by Duverger as the principal basis of consolidation, and studies the conditions under which strategic voting can change the sincere voting outcome and identifies the types of voters who should vote strategically under plurality and runoff rules. Three interesting findings can be drawn from the theoretical results. First, strategic voting is needed more often under plurality rule than under runoff rule to render the Condorcet winner the voting outcome. Second, under the plurality rule, strategic voting cannot ensure that a Condorcet winner will win and cannot even preclude a Condorcet loser from winning. Under the runoff rule, however, strategic voting ensures that the Condorcet winner will win, if one exists. Third, it is easier for a third candidate to enter the election and win the race under the plurality rule than under the runoff rule even if the third candidate is not a Condorcet winner.