PRSTV

PRSTV stands for Proportional Representation by the Single Transferable Vote. It is an electoral system used in multi-member districts to achieve proportional representation while allowing voters to support individual candidates rather than party lists. Voters rank candidates in order of preference, and seats are filled in districts that elect several representatives.

Counting in PRSTV centers on quotas and transfers. A quota determines how many votes a candidate must receive to be elected; most systems use the Droop quota, calculated as floor(n/(s+1)) + 1, where n is valid votes and s is the number of seats. Any candidate reaching the quota is elected, and their surplus votes are transferred to remaining candidates according to voter preferences, with fractional transfer values as needed. If no one meets the quota after transfers, the candidate with the fewest votes is eliminated and their ballots are transferred to the next preferred candidate still in contention. The process repeats until all seats in the district are filled. Ballots can become exhausted if all preferences are for candidates who are no longer in contention.

PRSTV generally yields proportional results across parties or groups, especially in larger multi-member districts, and supports minority and independent candidates by allowing voters to mix personal and partisan choices. However, it is more complex to count than plurality or closed-list systems, which can affect transparency and timetables for vote tabulation. Variants differ in quota choice, transfer rules, handling of exhausted ballots, and district magnitude, which in turn influence the level of proportionality achieved. Historically, PRSTV evolved from 19th-century Hare and Droop methods and is used in several jurisdictions, notably Ireland and Malta, as well as various Australian states and local governments.