Which system of voting is designed to achieve proportional representation in Northern Ireland?

The Single Transferable Vote (STV) is the system of voting designed to achieve proportional representation in Northern Ireland. This voting method allows voters to rank candidates in order of preference rather than selecting just one. In elections using STV, multiple representatives are elected from a single constituency, which reflects a broader spectrum of voter preferences compared to systems that rely on a single winner.

STV is particularly effective in multi-member constituencies, where the votes are counted in a way that aims to ensure that the overall representation of political parties aligns more closely with the proportion of votes they receive. Candidates who reach a certain threshold of votes are elected, and surplus votes can be transferred according to voters' subsequent preferences, thereby increasing the likelihood that many voices are represented in the legislative body.

Other voting systems such as First-past-the-post and the Alternative Vote tend to favor larger parties and often lead to outcomes where the distribution of seats does not accurately reflect the overall vote share of parties. Open List systems vary in terms of control over candidate selection and typically don't align with the proportional representation goal prevalent in Northern Ireland’s electoral strategy. Thus, STV stands out as the most suited mechanism for achieving proportional representation in this context.