A single-member district (SMD) is an electoral arrangement in which each geographic district elects exactly one representative to the legislature, usually by plurality (first-past-the-post). SMDs tend to favor large parties and produce two-party or two-party-dominant systems.
A single-member district (SMD) is exactly what it sounds like. The country is carved into geographic districts, and each district sends one person to the legislature. One district, one seat, one winner. Whoever gets the most votes in that district wins the seat, and everyone who voted for someone else gets no representation from that race.
That last part is the big idea for AP Comp Gov. Because only one candidate can win, SMDs reward big, broad parties and punish small ones. A party that wins 15% of the vote everywhere can end up with zero seats, because it never finishes first anywhere. This is why SMD systems push countries toward fewer, larger parties (a pattern political scientists call Duverger's law). Among the six AP Comp Gov course countries, the UK and Nigeria elect their lower houses using SMDs with plurality rules, while Mexico and Russia use mixed systems that combine SMD seats with proportional representation seats.
Single-member districts live in Unit 4 (Party and Electoral Systems and Citizen Organizations), where the CED asks you to explain how electoral rules shape party systems and representation. SMDs are one half of the course's central electoral-system contrast. SMD plurality systems tend to produce two-party or dominant-party legislatures, while proportional representation tends to produce multiparty systems. You can't fully explain why the UK has two dominant parties, or why Mexico's Chamber of Deputies mixes 300 district seats with 200 PR seats, without this term. It also connects backward to Unit 2, because the rules for electing a legislature shape how that institution behaves and which parties can hold the executive accountable.
Keep studying AP Comparative Government Unit 4
Plurality System (Unit 4)
These two almost always travel together. SMD describes the district (one seat each), and plurality describes the winning rule (most votes wins, no majority required). The UK's first-past-the-post system is the classic SMD-plus-plurality combo.
Proportional Representation (Unit 4)
PR is the structural opposite. Instead of one winner per district, parties get seats in proportion to their vote share, so a party with 15% of votes gets roughly 15% of seats instead of zero. The SMD vs. PR contrast explains most cross-country differences in party systems.
Majority System (Unit 4)
An SMD doesn't have to use plurality rules. A majority system requires the winner to clear 50%, often through a runoff. Nigeria's presidential election adds a twist by requiring geographic spread (25% of the vote in two-thirds of the states), showing that 'who counts as the winner' is a separate design choice from 'how many seats per district.'
Mixed Electoral Systems in Mexico and Russia (Unit 4)
Mexico and Russia hedge their bets. Mexico's Chamber of Deputies combines 300 SMD seats with 200 PR seats, and Russia's Duma splits 225 SMD and 225 PR. Mixed systems try to keep the local accountability of SMDs while giving smaller parties the access PR provides.
Expect multiple-choice questions that give you a description of an electoral system and ask you to identify it, or that ask you to predict the consequence of SMD rules (fewer parties, wasted votes, disadvantage for small parties). The 2019 Conceptual Analysis question asked about different types of party systems around the world, and SMDs are exactly the kind of cause you'd use in that answer, since SMD plurality rules help explain why some countries develop two-party systems while PR countries develop multiparty systems. On FRQs, don't just define SMD. Attach it to a course country (UK or Nigeria for pure SMD, Mexico or Russia for mixed) and explain the effect on representation or party competition.
SMD answers 'how many seats does each district have?' (one). Plurality answers 'how does someone win?' (most votes, even without a majority). They usually appear together as first-past-the-post, like in the UK, but they're separate design choices. An SMD could instead require a majority winner through a runoff. On the exam, keep the district structure and the winning rule distinct, because a question can test either one.
A single-member district elects exactly one representative per geographic district, so there is only one winner and every losing vote in that district goes unrepresented.
SMDs usually pair with plurality (first-past-the-post) rules, where the candidate with the most votes wins even without a majority.
SMD systems favor large parties and tend to produce two-party or two-party-dominant systems, while proportional representation tends to produce multiparty systems.
Among the AP Comp Gov course countries, the UK and Nigeria use SMD plurality for their lower houses, while Mexico and Russia combine SMD seats with PR seats in mixed systems.
SMD is about district structure (one seat), while plurality and majority are about winning rules, and the exam can test that distinction directly.
It's an electoral arrangement where each geographic district elects one representative to the legislature. The UK and Nigeria use single-member districts with plurality rules for their lower houses, while Mexico and Russia mix SMD seats with proportional representation seats.
Not quite. First-past-the-post is the combination of single-member districts plus a plurality winning rule. SMD only tells you each district has one seat; a system could instead require the winner to get a majority through a runoff.
They strongly encourage them. Because only the top vote-getter wins each seat, small parties rarely win anywhere, so voters and politicians consolidate around two big parties (this pattern is called Duverger's law). The UK's Conservative-Labour dominance is the standard example.
In an SMD, one candidate wins the whole seat and all other votes are wasted. Under PR, parties receive seats in proportion to their vote share, so a party with 20% of votes gets roughly 20% of seats. SMDs favor big parties; PR gives small parties a real path into the legislature.
The UK and Nigeria elect their lower houses entirely through SMDs with plurality rules. Mexico's Chamber of Deputies uses 300 SMD seats alongside 200 PR seats, and Russia's Duma splits 225 SMD and 225 PR seats in a mixed system.
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