Pros
- Wasted votes are minimised as both surplus votes and votes for losing candidates are redistributed
- Proportional system - mostly works very well to match party seats and votes so long as the constituencies are large enough (more proportionate with larger constituencies)
- Voters more likely to have an MP for whom they have voted for than under FPTP
- high level of voter choice. - voters can choose between candidates of the same party
- Potential to express intra-party preferences (candidates from different traditions within a party available to choose on the same constituency list)
- Offers voters the chance to choose popular candidates rather than simply their preferred party (not choosing unpopular candidates that parties have put forward).
- Group of representatives reflect the diversity of opinions in the area (true for any PR system)
- Voters can vote for independent candidates without worrying about wasting their vote
- It is a system where people use local knowledge to judge individual candidates at local level e.g for local government
- STV can offer protection against extremist/populist parties If they don't get a quota, then they can only win by being attractive to supporters of other candidates.
Cons:
- Garret FitzGerald , twice Ireland’s Taoiseach, criticised STV. arguing the multi seat nature led to "excessive localism" - because politicians of the same party competed against one another for votes, they were forced to act as glorified local ombudsmen/ errand runners rather than focusing on national policy. Both main parties supported a referendum to change from STV but the Irish people voted “No”. Other Irish politicians boast about their system.
- STV can potentially lead to extremist parties or populist candidates gaining representation. But if a candidate gets a quota of first preferences, they'll be elected in almost any PR system (if a candidate gets a quota of first preferences, there is no democratic reason for arguing against their election) National party vote thresholds are used by some countries for added protection so a minimum vote is required to gain any representation)
- Even with large multi-member constituencies, some smaller constituencies will not represent all parties (for example, a three- or four-seat constituency in a five-party system).
- The counting process in STV is complex and hard to explain to citizens, potentially endangering its legitimacy (but the process hasn’t been challenged, or its legitimacy endangered in practice)
- In Northern Ireland STV has not had as much impact as hoped in encouraging voting across sectarian dividing lines.
- Because it relies on transferred votes, it may promote bland “acceptable to all” policies
