Sweden & Duverger's Law

Blog 7: Sweden & Duverger’s Law

Jeff Merrell

In order to determine the validity of Duverger’s law about the number of effective political parties found in a state being a function of that state’s electoral rules, I decided to study one country about which I know almost nothing – Sweden.  I have a mission friend from Sweden, but know absolutely nothing about his native country and its politics.  Based on an evaluation of Sweden’s electoral rules and election results, I believe that Duverger’s law is, in fact, accurate.  The analysis performed in order to come to this conclusion is described below.

Effective Parties

Sweden’s legislative body is unicameral in nature and the most recent election held was in September 2010.  Only parties who register at least 4% of the nationwide vote are considered eligible for seat allocation and, in the 2010 election, eight parties surpassed that threshold (see the table below).  Based on the formula used to calculate the number of effective parties (N^eff), Sweden has 4.83 effective parties.

If Duverger’s law states that single-member-district plurality (SMDP) electoral systems lead to two effective parties and that proportional representation (PR) systems produce more than two, Sweden’s actual political environment is in line with that law.  Sweden’s electoral system is based on PR.

Sweden: Number of Effective Parties (2010)[1]
Party	Vote %	p2
Social Democratic Party (SAP)	30.66	0.094
Moderate Party (M)	30.06	0.09
Green Party (Mpg)	7.34	0.005
Liberal Party (FP)	7.06	0.005
Center Party	6.56	0.004
Sweden Democrats (SD)	5.70	0.003
Left Party (VP)	5.60	0.003
Christian Democrats (KD)	5.60	0.003
TOTAL Neff	4.83

  

Electoral Rules[2]

Below is a description of the various characteristics of Sweden’s electoral rules, including how elections are executed, as well as the following traits: district magnitude, formula, list structure, and thresholds.

Elections Overview.  Sweden’s Parliament (or Riksdag) is composed of 349 seats in total and elections for those seats are held every four years.  The country is divided into 29 multi-member constituencies, and 310 of those seats are allocated to each constituency.  The number of seats allotted to each constituency is revised every election cycle, depending on the number of voters in each constituency.  The seat distribution in each constituency is calculated using a modified version of the Sainte-Laguë format, which allows distribution to remain very close to each party’s proportion of votes.  The remaining 39 seats fall within an additional constituency that is based on nationwide voting (as opposed to the other 29 constituencies whose seat distributions are dependent on constituency-wide voting).

District magnitude.  The average district magnitude (total seats/total districts) is 349/30, or 11.6 seats per district.  In reality, however, that number is not true.  The more populated districts (or, in Sweden’s terms, constituencies) are allotted more seats and the last district is based on nationwide voting and receives 39 seats.

Formula.  As mentioned above, Sweden employs the Sainte-Laguë method in determining seat allocation.  It is modified from the original method by employing a greater divisor in its calculations, which ultimately tends to slightly favor larger parties over smaller ones.

List Structure.  Sweden employs a closed-party list system with preferential voting.  Each party has full discretion to rank its candidates in the desired order and voters can then use preference votes to any candidate(s) they desire.  Any candidate who receives a number of preference votes equal to or greater than eight percent of his/her party’s vote total is automatically placed at the top of the list.

Thresholds.  There are two threshold restrictions seen in Sweden’s electoral rules.  For political parties, they are required to obtain 4 percent of nationwide votes or 12 percent of the votes in a particular constituency in order to earn a seat in Parliament.  For individual candidates, they must receive at least eight percent preference votes of their party’s votes in a particular constituency in order to be awarded a seat based solely on preference votes.

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[1] The data for this table was obtained from the Inter-Parliamentary Union’s Parline website after searching for Sweden’s information. http://www.ipu.org/parline-e/reports/2303_E.htm.

[2] The information for this section was obtained from two sources: (1) the Inter-Parliamentary Union’s Parline website and (2) Wikipedia’s Electionworld.  http://www.ipu.org/parline-e/reports/2303_B.htm. http://en.wikipedia.org/wiki/User:Electionworld/Electionworld.