Raymond Miller, associate professor of political studies at Auckland University, looks at what MMP has delivered and the possible pitfalls of a referendum on electoral systems.
OPINION: It is hard to exaggerate the importance of this year's electoral referendum.
While the focus of public attention has been on the Rugby World Cup, and now the general election, any decision to replace or review MMP is likely to have significant implications for the future of the nation's politics.
There is no disputing the difference MMP has made to the way our political system works.
Under former electoral arrangements, small parties struggled to win any parliamentary seats.
Today, in contrast, seats are allocated in proportion to each party's share of the vote. Although the two major parties still win the lion's share, the monopoly with which they once exercised power has been greatly weakened.
But Parliament has also become more socially diverse, giving rise to inflated claims that it is a microcosm of society.
While levels of female and ethnic representation have increased, the pattern has been characterised by ebbs and flows in support, with the proportion of women MPs sitting stubbornly at one in three.
The under-30s and over-60s have yet to be represented in numbers anywhere approaching their voting strength.
Most significant of all, however, has been the effect of MMP on the composition and power of government.
Beginning with the failed National-NZ First coalition, fundamental changes have been made to the way government works, as illustrated by the constant need for multi-party consultation and cooperation.
Getting the Government's legislative agenda passed has necessitated a range of partnerships, from formal coalitions through to support agreements and memorandums of understanding.
The sheer complexity of these legislative arrangements has enhanced the power of Parliament relative to that of Cabinet.
Concern that the powers of government have been dangerously diminished has led to calls for MMP to be replaced.
Critics claim that, while progress has been made toward fairer representation, it has been at the cost of legitimate and effective government.
Whereas elections were once about choosing governments, it is argued that the power to decide has been usurped by party leaders.
Together with their advisers, they negotiate the terms of multi-party agreements behind closed doors.
Because small parties are at the centre of negotiations, their blackmail potential is frequently overstated, to a point where they are characterised as the "tail wagging the dog".
Little wonder then that MMP governments are criticised for being unstable and indecisive.
For most of the past 15 years, public opinion on the future of MMP has been evenly divided, with centre-left voters supporting the retention of MMP and centre-right voters favouring change.
However, the popularity of John Key's government has made MMP a more elusive target, especially for long-time National voters.
Because ACT's coalition ambitions were widely known prior to the 2008 election, the two parties could hardly be accused of doing post-election deals in smoke-filled rooms.
Moreover, through skilful inter-party management, the prime minister has been able to quell fears that the Maori and ACT parties pose a threat to government stability.
Indeed, for much of the past three years the Maori Party has been a model of cooperation and compliance. As a result, to publicly criticise MMP, as several National MPs have been tempted to do, risks detracting attention from John Key's prime ministerial success.
A further impediment to the anti-MMP campaign was the Vote for Change group's delay in announcing its preferred alternative to MMP.
While a return to the familiar First-Past-the-Post (FPP) system might have seemed an obvious choice (it is still used to choose our electorate MPs), it was finally decided to endorse the Supplementary Member (SM) System, probably on the grounds that, unlike FPP, its list seats would offer small parties some prospect of continued representation, if in substantially reduced numbers - only the 30 list seats are allocated proportionately.
As with FPP, SM increases the prospects of a single party majority government.
Because the electoral referendum coincides with the general election (unlike the 1992 electoral referendum), about 2.5 million voters will receive a referendum ballot.
If recent opinion polls are any guide, Part A could result in a slight majority for the retention of MMP.
The results of Section B are even more difficult to predict.
Because many voters will be unable to make an informed choice between the four alternatives to MMP, Section B threatens to be something of a lottery, with the first-named FPP option occupying the default position for the unprepared and unsuspecting.
Raymond Miller is associate professor of political studies at Auckland University.
- The Dominion Post