Why do small centrist parties often benefit from the single transferable vote system?

The single transferable vote (STV) system is a form of proportional representation that allows voters to rank candidates by preference. Under this system, small centrist parties often benefit because the vote-transfer mechanism allows them to capture support from voters whose first-choice candidates have already been elected or eliminated.12

In STV elections, when a candidate exceeds the required electoral quota, their surplus votes are redistributed to other candidates based on the voters' subsequent preferences. Similarly, if a candidate is eliminated due to having the fewest votes, their ballots are transferred to the voters' next choices. Because centrist parties often occupy a middle ground in the political spectrum, they are frequently the beneficiaries of these transferred votes from both sides of the political divide.132

Conversely, minor radical or extremist parties are typically penalized by this process, as they often lack the broad, cross-party appeal necessary to attract the secondary preferences required to secure a seat. This dynamic ensures that the final results reflect a broader consensus of voter preferences rather than just the initial support for a single party.123