Chile and Duverger’s Law

Duverger’s Law suggests that in countries where the electoral system is SMDP (Single Member District Plurality) there tends to be a two-party system. In the SMDP electoral systems, there are a certain number of allocated seats per voting district. In these districts, the party with the most votes wins the seat. The other type of electoral system is PR (Proportional Representation). In this system, the seats are allotted based on the proportion of the vote each party receives, so there tend to be multiple parties with candidates in elected positions. In this blog we will discuss calculate the effective number of parties and describe the electoral rules. Does Duverger’s Law remain true for Chile?
To calculate the effective number of parties in Chile, we looked at the latest election results. We found the proportion of seats that each party had received and then plugged the data into the following equation: N_eff=1/∑(p^2). The p is the proportion of seats of each party. You then square the proportion for each party, add them all together and then divide 1 by that sum. In the last election for the Chamber of Deputies, the election of 2009, the number of effective parties, after calculating the equation, was 2.74. When an electoral system has a number of more than 2, it means that it is a multiparty system, and thus it is with Chile. Though there are a few parties that are clearly more popular, Chile effectively has a multiparty system (Wikipedia, Chilean Parliamentary Election, 2009).
Now to assess Duverger’s Law in terms of Chile, we must look at their electoral rules. Since Chile clearly has a multiparty electoral system, it should follow that its system is PR. According to the Inter-Parliamentary Union website, Chile has “60 multi-member (2 seats) constituencies” so the district magnitude is two (IPU, Chile). No explicit threshold was mentioned, however “independent candidates require support of electorate equaling at least 0.5% of the votes cast in their constituency at the previous elections” (IPU, Chile). It says that the voting system is a “closed party-list majority system” with seats allocated in two ways. First, “if the majority party obtains more than two-thirds of the valid votes cast, it is entitled to the two seats of the constituency”, however, “if it obtains less than two-thirds, it is entitled to one seat and the second seat goes to the second-placed party” (IPU, Chile).  We can see here that Chile has somewhat of a hybrid system. If the majority party wins two-thirds of the vote, they receive the two seats for that district. This is clearly an SMDP electoral system. However, if the majority party receives less than two-thirds of the vote, they receive one seat, and the party with the next biggest amount of votes receives the second seat of the district. That is clearly PR. We see then that Chile has a hybrid system.
Chile has a multiparty and a hybrid electoral system. Though the system is a hybrid, the odds of the majority party receiving two-thirds of the vote is rare, thus in nearly all of the elections, the seats are allocated proportionally. Thus, in Chile’s case, Duverger’s Law holds true that in an SMPD ruled system, there tends to exist a two-party system, while in a PR system their tends to be multiple effective parties.



References


Wikipedia, Chilean Paliamentary Election, 2009, http://en.wikipedia.org/wiki/Chilean_parliamentary_election,_2009. (Accessed November 2, 2012).
Inter-Parliamentary Union. Chile. http://ipu.org/parline-e/reports/2063_B.htm. (Accessed November 2, 2012).