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Electoral Systems and Rules - AP Comparative Government and Politics Study Guide

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Learn with study guides reviewed by top AP teachers. This guide takes about 13 minutes to read.

Getting Started

An electoral system is the set of rules that determine how elections and referendums are conducted and how their results are determined. These rules shape how votes are translated into representation, influencing the party system, political competition, and government accountability. This chapter compares the diverse electoral systems and rules used to select national legislatures in China, Iran, Mexico, Nigeria, Russia, and the United Kingdom, explaining how these structures either foster competitive selection or advance specific political interests.

What You Should Be Able to Do

  • Compare the use of single-member districts in the United Kingdom and Nigeria with the mixed systems in Mexico and Russia.

  • Contrast the direct election methods in most course countries with the indirect method used in China.

  • Explain how electoral rules, such as candidate vetting in Iran or party list quotas in Mexico, affect political representation and competition.

  • Describe how proportional representation systems differ from plurality systems in their structure and likely outcomes.

Key Developments & Analysis

The primary distinction among electoral systems in the course countries is the degree to which rules are structured for open competition versus political control. This is most evident when comparing systems based on district type and the presence of additional rules that filter or shape outcomes.

Comparison: Plurality and Indirect Systems

DimensionUnited KingdomNigeriaChina
Legislative BodyHouse of CommonsHouse of Representatives & SenateNational People’s Congress (NPC)
Election MethodMembers are directly elected in single-member districts using first-past-the-post rules.Members of both chambers are directly elected in single-member districts.Members are selected indirectly through a series of local and regional elections.
Basis of RepresentationGeographic constituencies of roughly equal population.House seats are based on state population; Senate seats are distributed equally (3 per state).Representation is managed through a hierarchical series of people's congresses.
Why This MattersThe first-past-the-post (FPTP) rule, a type of plurality system, tends to produce clear majorities and supports a two-party system. In both the UK and Nigeria, this system creates a direct link between a representative and a specific geographic district, but it can also lead to governments elected with a minority of the national popular vote. China's indirect system ensures state control over the selection process, eliminating direct popular competition for national office and reinforcing the authority of the ruling party.

Comparison: Mixed and Controlled Systems

DimensionMexicoRussiaIran
Legislative BodyCongress of the Union (Chamber of Deputies & Senate)State DumaMajles
Electoral SystemA mixed-member system combining single-member districts (SMD) and proportional representation (PR).A mixed-member system with half of the representatives from SMDs and half from PR with a threshold.A direct election system using a mix of single-member and multimember districts.
Key Rules300 deputies by plurality in SMDs; 200 by PR party list. Gender quotas apply to party lists.PR elections use a party-list system with a minimum vote threshold to gain seats.Candidates must be vetted by the Guardian Council. A second round of voting may be required.
Why This MattersMexico’s system is designed to balance geographic representation (from SMDs) with ideological representation (from PR), promoting a multiparty system. Russia's return to a mixed system, particularly the PR threshold, is a rule change that can be used to limit the representation of smaller opposition parties and advance the interests of the dominant party. Iran's system, while featuring direct elections, severely limits competition through the ideological vetting of candidates, ensuring the legislature reflects the state's religious principles rather than a broad political spectrum.

Data & Organization Tools

Concept-to-Countries Matrix

Election Method for National Legislature

MethodCountriesDescription
Direct ElectionIran, Mexico, Nigeria, Russia, UKCitizens vote directly for legislative representatives.
Indirect ElectionChinaCitizens elect local officials who then select representatives for higher-level bodies.

Primary District Type

District TypeCountriesDescription
Single-Member District (SMD)UK, NigeriaThe country is divided into districts, each electing one representative, typically by plurality vote.
Mixed (SMD & PR)Mexico, RussiaA portion of seats are filled by representatives from SMDs, and the rest are filled using proportional representation.
Mixed (SMD & MMD)IranUses a combination of single-member and multimember districts.

Rules Affecting Representation & Competition

RuleCountryDescription
Candidate VettingIranThe Guardian Council approves all candidates for office, limiting voter choice.
PR ThresholdRussiaA party must win a minimum percentage of the national vote to receive any party-list seats.
Gender QuotasMexicoParties are required to include a certain percentage of women on their PR party lists.
Reserved Minority SeatsIranA small number of seats in the Majles are reserved for specified non-Muslim minorities.

Institution–Actor–Function Map

InstitutionKey Actor(s)Electoral Function
Guardian Council (Iran)Council Members (clerics and jurists)Vets and approves/disqualifies candidates running for the Majles.
National People's Congress (China)Local & Regional CongressesSelects members for the national legislature; does not involve competitive popular election.
Congress of the Union (Mexico)Political Parties, VotersParties create candidate lists (for PR) and nominate district candidates; voters elect representatives through two different ballot types (SMD and PR).
House of Commons (UK)Voters, Political PartiesVoters in single-member districts elect one representative via the first-past-the-post method.

Country Anchors Bank

  • UK's First-Past-the-Post (FPTP) System: The classic example of a single-member district plurality system. It provides a clear link between a Member of Parliament and their constituency but often exaggerates the seat share of the largest parties.

  • Mexico's Gender Quotas: A key rule applied to the proportional representation party lists for the Congress of the Union. This policy is a strong example of how electoral rules can be designed to increase the representation of specific demographic groups.

  • Iran's Guardian Council Vetting: The most significant rule limiting electoral competition in Iran. The Council's power to disqualify candidates ensures that only those aligned with the regime's ideology can run for the Majles.

  • China's Indirect NPC Elections: The sole example among the course countries of an indirect election system for a national legislature. This process highlights a system where selection by party-controlled bodies replaces popular competition.

  • Russia's Duma Electoral Threshold: A rule requiring parties to secure a minimum percentage of the national vote to win seats from the proportional representation list. This mechanism can be adjusted to consolidate power by excluding smaller opposition parties from the legislature.

  • Nigeria's State-Based Senate Representation: The Nigerian Senate has three members directly elected from each of the 36 states, regardless of population. This rule demonstrates how electoral systems can be structured to represent federal units equally, balancing the population-based representation of the House.

Skill Snapshots

  • Comparison: The UK's pure first-past-the-post system encourages a two-party system, whereas Mexico's mixed-member system promotes a multiparty system by allowing smaller parties to gain seats through proportional representation.

  • Comparison: While both Iran and Nigeria hold direct elections, Iran's system severely restricts competition through candidate vetting by the Guardian Council, whereas Nigeria's features open competition between two major parties.

  • Comparison: All course countries except China use some form of direct election for their national legislature; China's indirect system of selection by lower-level congresses is unique and demonstrates a lack of competitive selection.

  • Mechanism: In Iran, the Guardian Council's vetting process → limits the ideological diversity of candidates for the Majles.

  • Mechanism: In Mexico, the use of gender quotas on party lists → has led to a significant increase in female representation in the legislature.

  • Mechanism: In the UK, the use of single-member districts with FPTP rules → often results in a majority government in the House of Commons even if the winning party receives less than 50% of the popular vote.

  • Change Over Time (Russia):

    • Baseline: Russia has experimented with different electoral systems for the Duma.

    • Change: The system has returned to a mixed model where half the seats are from single-member districts and half are from proportional representation.

    • Change: The threshold for the proportional representation portion has been adjusted over time.

    • Continuity: Changes to the electoral system are frequently used to advance the political interests of the ruling elite and manage political competition.

Common Misconceptions & Clarifications

  • "Direct elections" do not always mean "democratic." Iran holds direct elections for the Majles, but the system is not considered fully competitive due to state-controlled candidate vetting.

  • Not all "mixed" systems are identical. Mexico's system is designed to increase representation for smaller parties, while Russia's mixed system, with its PR threshold, has been used to consolidate the power of the dominant party.

  • China has elections, but not for national office. The indirect selection of the National People's Congress is fundamentally different from the competitive, direct elections in other course countries.

  • Proportional Representation (PR) rarely achieves perfect proportionality. It aims to translate a party's vote share into a similar seat share, but features like electoral thresholds can distort this outcome.

One-Paragraph Summary

Electoral systems are the foundational rules that translate citizen votes into political power, and they vary significantly across the six course countries. At one end of the spectrum, the United Kingdom and Nigeria use single-member, first-past-the-post systems that foster direct geographic representation and tend toward two-party dominance. In the middle, Mexico and Russia employ mixed systems that combine single-member districts with proportional representation, attempting to balance local accountability with ideological diversity, though Russia has used its rules to consolidate power. At the other end, Iran and China demonstrate systems where rules limit competition; Iran uses direct elections but filters candidates through the Guardian Council, while China forgoes direct national elections entirely in favor of an indirect selection process. These systemic differences fundamentally determine the nature of political competition, the diversity of representation, and the relationship between citizens and the state.