STV

Multi-winner ranked ballot. Surplus and eliminated votes transferred to next choice until Droop quota reached by winners (k=seats available):

\frac{\text{total votes}}{k+1}

Used in NI assembly, NI local governments, Scotland local governments

Disadvanages of STV

Complexity

  • Harder for voters to understand than a simple X in the box
  • Counting is slow – multiple rounds of transfers, results can take days
    • e.g. Scottish local elections 2007 (introduced alongside e-counting) saw thousands of spoilt ballots and count delays

Weakens constituency link

  • Multi-member constituencies are larger geographically
  • Voters share several MPs/councillors rather than one clear representative
    • less clear who to hold accountable, “passing the buck” between reps

Can still produce disproportionality

  • Only proportional if constituency magnitude (seats per constituency) is large enough
  • Small magnitudes (e.g. 3-5 seats, as in NI/Scotland) still favour larger parties somewhat

Intra-party competition

  • Same-party candidates compete against each other for preference votes
  • Can lead to internal party rivalry, factionalism, focus on personality over policy

Can produce coalition/weak government

  • Proportional outcomes make single-party majorities unlikely
  • Counterpoint to FPTP’s “strong government” advantage
    • e.g. NI Assembly power-sharing arrangements, prone to collapse (e.g. 2017-2020 suspension)

Advantages of STV

Proportionality

  • Seats won closely reflect vote share, few wasted votes compared to FPTP
  • Smaller parties can gain representation without needing geographically concentrated support

Voter choice

  • Voters rank candidates, including choosing between candidates of the same party
  • Reduces need for tactical voting — can rank sincerely and still have vote count via transfers

Reduces safe seats

  • Multi-member seats mean most areas elect a mix of parties
  • Discourages complacency, keeps more seats competitive

Greater choice of representative

  • Constituents can approach any of their multiple reps, not just the “winner”
  • Useful where a constituent’s own MP/councillor is unresponsive or from an opposing party
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