Proportional representation (PR) is an electoral system that allocates legislative seats to parties based on their share of the national vote, which tends to increase the number of parties in the legislature and the election of women and minority candidates (DEM-2.B.1).
Proportional representation is an electoral system where a party's share of the vote translates directly into its share of legislative seats. Win 30% of the vote, get roughly 30% of the seats. Voters usually pick a party rather than an individual candidate, and parties fill their seats from ranked candidate lists.
The AP exam cares less about the mechanics and more about the consequences. Per the CED (DEM-2.B.1), PR tends to increase the number of political parties in national legislatures, because small parties can win seats without winning any single district. It also tends to increase the election of women and minority candidates, since parties can balance their candidate lists instead of betting everything on one candidate per district. Among the course countries, Mexico and Russia use mixed systems that combine PR seats with single-member district seats, so PR isn't just theory, it's how real seats get filled in the Chamber of Deputies and the Duma.
PR lives in Unit 4 (Party and Electoral Systems), specifically Topic 4.2, where learning objective AP Comp Gov 4.2.A asks you to explain how election rules serve different regime objectives. PR is one half of the most-tested contrast in that topic. PR systems prioritize broad ideological representation, while single-member district plurality systems (DEM-2.B.2) prioritize constituency accountability and tend to produce two-party systems. You also need PR for AP Comp Gov 4.1.A, describing electoral systems in the course countries, since Mexico and Russia both allocate some legislative seats through PR. The concept spills into Unit 2 (legislative structures and coalition government) and Unit 1, where PAU-1.C.2 notes that democratic electoral systems can accommodate ethnic and social diversity. PR is one of the main tools for doing exactly that.
Keep studying AP Comparative Government Unit 1
Single-Member District Plurality Systems (Unit 4)
This is PR's mirror image and the contrast the exam loves. SMD plurality (used in the UK) elects one winner per district, which squeezes out small parties and produces two-party systems with strong constituency accountability. PR trades that local accountability for proportionality. Every effect of one system is basically the reverse of the other.
Legislative Systems in Mexico and Russia (Unit 2)
PR isn't abstract in this course. Mexico's Chamber of Deputies and Russia's Duma both fill seats through mixed systems that combine PR with single-member districts. When a question asks how a course country's legislature is elected, PR is often part of the correct answer.
Democratization (Unit 1)
PAU-1.C.2 says democratic electoral systems can accommodate ethnic and social diversity. PR is how that happens in practice. By giving smaller groups seats proportional to their numbers, PR pulls ethnic and ideological minorities into the legislature instead of leaving them shut out.
Parliamentary Systems and Coalition Government (Unit 2)
PR usually means no single party wins a majority, so parties have to form coalitions to govern. That makes PR a natural fit for parliamentary systems, where the legislature picks the executive, and explains why multiparty parliaments often have less stable cabinets.
Multiple-choice questions usually test consequences, not mechanics. Expect stems like "Which best explains why PR systems elect more women to national legislatures?" or "What would most likely happen if the UK switched from SMD plurality to PR?" The answer almost always traces back to DEM-2.B.1: more parties, more minority and women candidates. On free-response questions, PR shows up in party-system comparisons. The 2019 Comparative Analysis question on different types of party systems is the classic setup, where you explain how electoral rules shape whether a country has two parties or many. PR also supports the 2018 SAQ on social cleavages, since PR is the mechanism that lets cleavage-based parties (ethnic, religious, regional) actually win seats. Your job on the exam is to connect the rule to the outcome. Don't just define PR; explain what it causes.
In PR, voters choose a party and seats are split by vote share, so a party with 15% of the vote gets seats. In SMD plurality (the UK's system), one candidate wins each district by getting the most votes, and a party with 15% spread evenly across the country could win zero seats. PR maximizes proportionality and party diversity; SMD maximizes accountability to a local constituency and pushes toward two big parties. If a question mentions "strong constituency service" or "geographic representation," that's SMD, not PR.
Proportional representation allocates legislative seats based on each party's share of the national vote, so seat totals roughly match vote totals.
PR tends to increase the number of parties in the legislature and the election of women and minority candidates (DEM-2.B.1).
Single-member district plurality systems do the opposite, promoting two-party systems with strong constituency accountability (DEM-2.B.2).
Mexico and Russia use mixed electoral systems that fill some legislative seats through PR and others through single-member districts.
Because PR rarely gives one party a majority, it often leads to coalition governments, especially in parliamentary systems.
PR helps democratic systems accommodate ethnic and social diversity by giving smaller cleavage-based parties a path into the legislature.
It's an electoral system where parties win legislative seats in proportion to their share of the vote. A party with 25% of the vote gets about 25% of the seats. The CED ties it to more parties in the legislature and more women and minority candidates elected (DEM-2.B.1).
No. PR makes coalition governments more likely because single-party majorities are rare, and coalitions can be less stable than single-party rule. But many PR democracies govern through durable coalitions, so "PR equals chaos" is an overstatement the exam won't reward.
PR distributes seats by party vote share across multi-member constituencies, while SMD plurality elects one winner per district. PR produces multiparty legislatures with broad representation; SMD (used in the UK) produces two-party dominance with strong local accountability and geographic representation.
Mexico and Russia both use mixed systems that combine PR seats with single-member district seats in their lower houses (the Chamber of Deputies and the Duma). The UK, by contrast, uses pure SMD plurality for the House of Commons.
In PR, parties run lists of candidates instead of one candidate per district, so they can place women throughout the list without risking a single seat on any one candidate. This is a directly tested point from DEM-2.B.1 and a common multiple-choice stem.