Blog 7: Duverger's Law

            Duverger’s Law states that the effective number of parties in any electoral district is a function of the electoral rules: SMDP rules produce two effective parties, while proportional representation rules allow for more.  In my study of Mexico, I found this law to be true because Mexico utilizes both sets of rules in a hybrid system that results in three effective political parties.

            Mexico has a bicameral system with two chambers that make up the Congress of the Union.  The Chamber of Deputies is the lower chamber of the Congress and is made up of 500 members which are elected for a three-year term of office, and may not be immediately re-elected. The electoral system that functions is a sort of hybrid that combines elements SMDP rules as well as PR rules. A total of 300 seats are elected in single member districts by the first-past-the-post method; every federal entity has a minimum of two single-member seats.  The remaining 200 members are elected by proportional representation in 5 multi-state constituencies, or electoral districts, with 40 seats each.  In order to participate in the apportionment of Chamber of Deputies proportional seats, a political party must field candidates in at lest 200 single-member districts, and receive at least two percent of the total number of votes cast for proportional lists, including invalid ballots. However, no political party may receive more than 300 seats (www.electionresources.org). This shows how the SMDP rules can be combined with PR rules to effectively compose an electoral system. 

            Mexico has a multi-party system that is made up of seven nationally recognized political parties by the Federal Electoral Institute. However, historically there have been three parties that have dominated the political scene: the National Action Party which is a right of center party, the Institutional Revolutionary Party which is a centrist party composed of right leaning and left leaning members, and the Party of the Democratic Revolution which is a left of center party. Using the formula we discussed in class, the number of effective parties in Mexico was calculated to be a little bit more than three. In the July 2012 election, the Institutional Revolutionary Party received 212 total seats, the National Action Party received 114 total seats, and the Party of the Democratic Revolution received 104 total seats, which is a significantly greater amount of seats than all of the other parties that received a portion of the seats (www.ipu.org). This calculation validates the other sources that claim that Mexico has historically been dominated by three political parties.  This calculation also provides evidence that backs up the theory behind SMDP rules as well as PR rules.

 SMDP rules generally allow for two dominating political parties whereas PR rules generally allow for more competition between a greater number of parties.  The fact that Mexico has three effective parties shows how it is a hybrid because the results for the number of effective parties lies somewhere in between the general results of the two sets of rules.  If SMDP rules were the only rules set in place we would see two dominating parties whereas if strictly PR rules were used we would see a large amount of effective parties.  Overall this hybrid seems to be an effective approach to elect the members of the Chamber of Deputies.

                                                        Works Cited

http://www.electionresources.org/mx/index_en.html.  Federal Elections in Mexico. Manuel Alvarez Rivera. November 1, 2012

http://www.ipu.org/parline-e/reports/2211_E.htm. Inter-Parliamentary Union: Mexico. November 1.2012

http://en.wikipedia.org/wiki/Congress_of_Mexico

http://en.wikipedia.org/wiki/Elections_in_Mexico