This will surprise even many STV supporters.
Although opponents claim that a disadvantage of STV is that it is less party proportional than some other systems, the Ministry of Justice reported on 24 January 2008 that it was more party proportional than any other system used in the UK.
Today is the tenth anniversary of the Ministry of Justice’s Review of Voting Systems*.
Paragraph 15 of the Summary states:
“STV for the Northern Ireland Assembly has led to the most [party] proportional distribution of seats in any UK election.”
As the review states in Paragraph 21 of the summary:
“All the newly introduced voting systems have achieved a greater degree of [party] proportionality than FPTP, although only STV in Northern Ireland has achieved what academic observers consider to be close to genuine [party] proportionality.”
According to Paragraph 5.112 in Chapter 5 of the Report:
“All [STV] election results in Northern Ireland show a strong match between first preference votes cast and the allocation of seats.”
These quotations nail the accusation by some that STV is less party proportionate than other PR systems.
In any case, STV offers many other advantages that other PR systems do not. Not least of those is that STV can provide proportionality not only between political parties but also between any other groupings that matter to voters; e.g. Remain and Brexit or for and against a local development.
STV also increases voter power, maximizes voter choice and ensures that all MPs are elected the same way so there are no disputes about whether some are elected more legitimately than others. In addition, it makes them more accountable to voters and less to party whips.
*The Governance of Britain
Review of Voting Systems:
the experience of new voting systems in the United Kingdom since 1997