Notes
Electoral systems
- Single-member district plurality (SMDP), or "first past the post": the candidate with the most votes wins each district. It tends to produce two-party systems (Duverger's law) and can give a party a parliamentary majority without a majority of votes (the UK House of Commons).
- Proportional representation (PR): parties get seats in proportion to their share of the vote. It helps smaller parties and often leads to multiparty systems and coalitions.
- Mixed systems: some seats by SMDP, some by PR (Mexico's Chamber of Deputies, Russia's Duma).
- Two-round systems hold a runoff if no one gets a majority (Iran's presidential elections; Russia's).
- Nigeria's president must win a plurality plus at least 25% of the vote in two-thirds of the states.
Party systems
- One-party: China (the Chinese Communist Party).
- Dominant-party: Russia (United Russia); Mexico under the PRI until 2000 (later the PAN and now Morena have won).
- Two-party: the UK (Conservatives and Labour), though smaller parties like the Liberal Democrats and the Scottish National Party win seats.
- Multiparty: Mexico today; Nigeria (the APC and PDP lead).
- In Iran, the Guardian Council vets and disqualifies candidates, limiting real competition.
Citizen organizations
- Pluralism: many groups compete for influence (the UK).
- Corporatism: the state recognizes and works with a few official groups (Mexico's PRI historically linked unions and peasant groups to the party; China's state-run unions).
- Social movements push for change (Mexico's protests against violence, environmental movements).
- Patron-clientelism trades favors for political support (common in Nigeria and historically in Mexico).
Practice
Smaller parties struggle to win districts.
It helps smaller parties gain seats.
Each constituency elects one MP.
The PRI held the presidency for 71 years.
It vets candidates for loyalty to the system.
Historically, Mexico's PRI incorporated unions.
It's common where institutions are weak.
About 300 seats come from districts and 200 from PR lists.
Free response
Write your answer first, then open the scoring guide.
Free-response question
Answer (a), (b) and (c).
(a) Describe ONE difference between single-member district plurality and proportional representation.
Show the answer and scoring guide
In SMDP, the candidate with the most votes in each district wins the seat; in PR, parties win seats in proportion to their share of the national vote.
Check off the points you earned:
(b) Explain how the UK's electoral system affects its party system.
Show the answer and scoring guide
SMDP favors the two largest parties (Conservatives and Labour), making it hard for national third parties to win seats proportional to their votes, though regional parties like the SNP can win.
Check off the points you earned:
(c) Explain how competition in Mexico's party system has changed since 2000.
Show the answer and scoring guide
The PRI lost its dominance; the PAN won the presidency in 2000 and 2006, the PRI returned in 2012, and Morena won in 2018 and 2024, creating a multiparty, competitive system.
Check off the points you earned: