Estás segura de que es proporcional puro? No conozco el sistema de elección en Irlanda, pero parece que al elegir puedes marcar a varios candidatos. Ese single transferable vote se asemeja al sistema mayoritario británico, pero lo corrige hacia la proporcionalidad. Si lo entiendo bien. Me parece que es un sistema mixto, no proporcional puro.
Pero vamos, también reconozco que no conozco el sistema irlandés. He googleado y leo esto:
"A quota (the minimum number of votes that guarantees election) is calculated by a specified method (usually in STV using
the Hare or Droop methods), and candidates who accumulate that many votes are declared elected. In many STV systems, the quota is also used to determine surplus votes, the number of votes received by successful candidates over and above the quota. Surplus votes are transferred to candidates ranked lower in the voters' preferences, so they would not be wasted by remaining with a candidate who does not need them.
If seats remain open after this first count, surplus votes are transferred to generate the necessary winners. The specific method of transferring votes varies in different systems (see
§ Vote transfers and quota). Transfer of any existing surplus votes is done before eliminations of candidates. This prevents a party from losing a candidate in the early stage who might be elected later through transfers.
[2] When surplus votes are transferred under some systems, the vote is apportioned fractionally to different candidates. In others, transfers are done using whole votes."
Si lo entiendo bien es una corrección del sistema mayoritario, hacia más proporcionalidad, haciéndolo por tanto mixto, pero partiendo de mayoritario.
Una impresión, ya te digo, no conozco el sistema irlandés más allá de lo que ahora he googleado.