How it works
MMP gives voters two votes - one for their preferred political party, and the other for the MP they want to represent their electorate.
Parties have to get a minimum of 5 per cent of the vote or win at least one electorate seat to get their share of seats in Parliament.
Parties rarely win enough votes to govern alone, and coalitions are a common feature of New Zealand governments.
The result is a Parliament in which a party's share of seats largely reflects its proportion of the national vote.
Until MMP was voted in, Kiwis had one vote under FPP - a system where candidates with the most votes won, regardless of whether they had 50 per cent.
Major parties tended to win a larger proportion of parliamentary seats than their share of votes, while smaller parties were largely sidelined.
Electoral shakeup
Catalysts for electoral reform began to stir in the 1950s when public confidence in politicians and the two-party system began to erode.
Over the following decades, economic uncertainty and social upheaval helped give traction to the idea that Kiwis were not being accurately represented.
Despite winning decent chunks of the vote, many smaller parties were being excluded from Parliament altogether, causing significant voter disillusionment.
Canterbury University political science lecturer Bronwyn Hayward says many people felt FPP unfairly inflated the vote of some parties.
"For example, in 1978 and 1981 Labour actually won more votes but National still won the election."
However, other concerns played an equal hand in the push for change.
"It wasn't just frustration that a party like National could win unfairly. There was also, equally, huge anger at Labour, which had been elected in 1984 and then embarked on major economic and social reforms in a way that was sprung on the public."
There was no way to hold MPs to account once they were elected, prompting calls for a system in which people had more of a voice, Dr Hayward says.
In 1993, Kiwis voted in a referendum to change the voting system to MMP - marking the country's biggest electoral change since women got the vote a century earlier.
The overhaul intended to give parties representation that was proportionate to their overall vote, and to give a voice to smaller parties and minorities.
But it hasn't all been plain sailing, and the looming election is bringing some of the biggest gripes about MMP to the forefront.
Perceived failures
One major complaint is the merits of the "coat-tailing" provision, which allows smaller parties that have not met the 5 per cent threshold to bring MPs into Parliament on the "coat-tails" of an MP who has won an electorate seat.
The clause also permits larger parties to forge deals to help smaller parties over the line, like National's deal with Act in Auckland's Epsom seat in 2011.
Former Act leader and Epsom MP John Banks' infamous "cup of tea" with Prime Minister John Key ahead of the last election has become synonymous with the practice, which many now want to see canned.
Following a 2011 referendum on MMP, which saw it retained, the Electoral Commission called for the coat-tailing clause to be thrown out.
"The one electorate seat threshold ... runs counter to some of the most fundamental principles of the MMP voting system, including that all votes should be of equal value, the primacy of the party vote in determining election outcomes, and fairness of results," the commission said at the time.
The electorate vote could be used to "significantly influence" the make-up of Parliament by bringing in list MPs who would not otherwise be elected, it said.
Should it win the election, Labour is promising to abolish the coat-tailing clause within 100 days of taking office.
Another of MMP's controversial features is the provision known as "waka-jumping" - when a list MP is ejected from their own party but can remain in Parliament.
National Party delegates last year voted to ask the Government for a new law that would force these MPs out, amid fears disgraced junior MP Aaron Gilmore would be allowed to stay in Parliament despite having been kicked out of the National Party for his boozed rant to a waiter. The request is currently before the Constitutional Advisory Panel.
A diverse community
Political science lecturer at Canterbury University Lindsey MacDonald says MMP made Parliament look much more like New Zealand, but this has had a double effect.
"It makes clear that we are a diverse community with multiple views on any subject and that in order to knit together a solution, everybody has to be included.
"But it's also raised and put in front of us that we're much more diverse than we're realistically comfortable with.
"MMP really shoves in our faces that politics is how we sort things. You have to have politics and you have to work with everybody."
The rise of transparency and representation has brought with it an unfortunate drop in voter participation.
Statistics New Zealand figures show voter turnout dropped from 88.3 per cent in the first MMP election in 1996 to 74.2 per cent in the 2011 election.
"We used to just turn up and vote. And now we're confronted with the dirty business that is politics, we don't really like it so we're not voting."
Put to the people
The public had their say in a national referendum on MMP in 2011.
While New Zealanders voted to keep the system, the referendum review included a number of recommendations on how the system could be improved.
These included an end to the coat-tailing clause and lowering the 5 per cent party vote threshold to 4 per cent.
However, these have been largely ignored by the Government.
Justice Minister Judith Collins told Parliament last year that consensus was required for electoral reform, "and there is no consensus for any change".
But the decision to reject the recommendations was met with backlash from critics.
Accountability
Ahead of the referendum, a group called "Vote for Change" lobbied against MMP.
While the group has since dissolved, former spokesman and constitutional lawyer Jordan Williams still says our current system's fundamental flaw is a lack of accountability.
"Every system has its flaws but at least politicians think, 'I'd better do what the voters want, otherwise I'll lose my seat'.
The trouble with MMP is too often it's, 'I have to do what my party wants, otherwise I'll get a low list position and lose my seat'."
Even though Kiwis voted to keep the system, we are becoming increasingly more "annoyed" with the political process, he says.
A good example of this is the recent union of the Internet and Mana parties.
"You've effectively got a rich foreigner [Kim Dotcom] who has created his own political plaything, joined up with a far left party," he says.
"It certainly is taking the position that everyone's views matter in an MMP system to the utmost extreme." APNZ
