Electoral systems are treated as procedural detail. They determine more about political outcomes than most policy debates do.
First past the post
Single-member districts where the candidate with most votes wins.
Simple, produces a clear local representative, and translates vote shares into seat shares very unevenly.
A party with support spread evenly across districts can win a substantial vote share and few seats. A party with concentrated support does far better.
Which tends to produce two dominant parties, since voters anticipate this and vote strategically, and smaller parties struggle to convert votes into representation.
Proportional systems
Seats allocated in proportion to votes, generally within multi-member districts or nationally.
Which produces closer correspondence between vote share and seat share, and generally more parties.
Coalition government becomes the norm rather than the exception, since single-party majorities are rarer.
Thresholds — a minimum vote share to receive any seats — are common and exist to limit fragmentation, and they exclude parties below them entirely.
Mixed systems
Combining district representatives with proportional adjustment.
Which attempts to preserve local representation while correcting overall disproportionality.
Whether the proportional element fully compensates depends on the design, and systems described as mixed vary enormously in how proportional they actually are.
Preferential and ranked systems
Voters rank candidates, and preferences transfer as candidates are eliminated.
Which ensures the winner has majority support among those expressing a preference, and reduces the incentive for strategic voting.
In single-member form it does not improve overall proportionality. In multi-member form it can substantially.
Districting
Where boundaries are drawn affects outcomes independently of the system.
Manipulating boundaries for partisan advantage is possible in any district-based system, and it has a long documented history.
Independent boundary commissions are the standard response, and their independence and criteria vary considerably between countries.
Measures of partisan bias in district maps have been developed and used in litigation, with courts in different jurisdictions reaching different conclusions about whether they are justiciable.
What each system encourages
Majoritarian systems tend toward decisive government with less consensus-seeking, and toward alternation between two blocs.
Proportional systems tend toward coalition, negotiation and policy continuity across governments, with slower change.
Which is better depends on whether you value decisiveness or representation, and that is a value judgement rather than a technical question.
Turnout
Comparative research finds higher turnout in proportional systems on average, with the proposed explanation being that fewer votes are wasted.
Compulsory voting, used in some countries, produces the highest turnout and raises its own questions about coercion and about the informedness of compelled votes.
Reform
Electoral system change is rare because it is decided by those the current system elected.
Referendums on reform have been held in several countries, generally rejecting change, with campaigns focusing on complexity and on coalition instability.
Where change has occurred it has usually followed a crisis of legitimacy rather than a technical argument, which is consistent with how institutional change generally happens.
Candidate selection
Where a considerable amount of the real choice happens and which receives little attention.
In safe districts under majoritarian systems, the party's selection effectively determines the representative.
Which means the selectorate — party members, a committee, or a primary electorate — matters more than the general election in those places.
Systems with closed party lists give parties even more control, since voters choose a party and the party determines the order.
Open list systems return that choice to voters, which changes candidate behaviour toward personal rather than party appeal.
Campaign finance
Regulation varies enormously and interacts with the electoral system.
Spending limits per candidate, per party, or per period all exist in different combinations.
Third-party spending by organisations not standing for election is where most of the regulatory difficulty concentrates.
Public funding of parties exists in many systems, generally allocated by prior vote share, which advantages established parties.
Timing
Whether the government can choose the election date, or whether terms are fixed, has measurable effects.
Discretionary timing allows governments to call elections at favourable moments, which research suggests is worth a measurable advantage.
Voter registration
An administrative matter with substantial effects on who actually votes.
Automatic registration, where the state enrols eligible citizens, produces higher registration than systems requiring individual application.
Registration deadlines, identification requirements and address-based enrolment all affect participation, and the effects fall unevenly across groups.
Which is why these administrative rules are politically contested in a way that appears disproportionate to their technical nature, and the contest is rational given the effects.
Postal and early voting
Availability affects turnout and composition of the electorate.
Where postal voting is universal, turnout is generally higher, and the administrative requirements for verification are substantial.
Early in-person voting spreads demand and reduces queues, which matters where polling place capacity has been a source of disenfranchisement.
Rules on these have been among the most contested electoral changes in several countries.