KEY POINTS:
MMP means "more meddlesome parties". So some think who want shot of mixed-member proportional voting so the big old parties can have a freer hand. But this election the small party in the spotlight does not depend on proportional votes.
The Maori Party, which might be the pivot in post-election negotiations, wins electorate seats, not list seats, so it doesn't depend on MMP. Those seats could be pivotal even under first past the post (FPP): in 1946-69 and in 1957-60 the then four Maori seats were critical to Labour governments' majorities.
In 2005, the Maori Party won four of the seven Maori electorate seats, one more than its party vote entitled it to - that is, the party won one "overhang" seat.
This election, it seems set to win five to seven electorate seats. That would give it from two to four "overhangs", depending on its party vote - in recent polls barely enough to warrant three seats.
Overhangs change Parliament's arithmetic by raising the total number of MPs by one for every overhang. Two or three overhangs would lift the total from 121 now to 122 or 123.
The majority needed for the Budget and for legislation would rise from 61 now to 62. Four overhangs (124 MPs) would push the majority to 63.
In addition, Jim Anderton's Progressive party might score such a low party vote as to make him an overhang.
Compared with a strictly proportional system which assigns seats only by a single party vote, it could be said that parties with overhangs are over-represented.
For a different reason, the same could be said of Act and United Future.
They fell far short of the 5 per cent hurdle in 2005 but were assigned seats proportional to their party votes because their leaders won electorate seats.
Such quirks have encouraged MMP critics to assert that small parties have disproportionate influence - that they are tails wagging the dog - though the two parties that extracted the most from the government in the 2005-08 term, New Zealand First and the Greens, cleared the 5 per cent hurdle and do not have electorate seats.
One set of parties has lost traction with voters: the outsiders. No new party has entered Parliament at an election since 1996 (the Greens came in in 1999 but had been part of the Alliance in the previous term). Only if Taito Phillip Field holds Mangere will a distinct new party enter Parliament this time.
The "wasted" vote for parties that don't win seats has fallen from 7.5 per cent in the first MMP election in 1996 to 1.3 per cent in 2005. Polls suggest a similar wasted vote this time, unless New Zealand First fails to win any seats.
If its party vote was just over 4 per cent (as in 1999), that would push the wasted vote up to about 5.5 per cent.
Taking all that into account, what does National need for a majority?
Assume Act and United Future get four seats between them: three plus one or two plus two. Both are sure-fire National backers. That would leave National needing 58 seats for a majority of 62 (assuming there are two or three overhangs).
If New Zealand First is not in Parliament and the wasted vote is about 5.5 per cent, National would need just under 46 per cent of the party vote to get 58 seats.
Add 0.8 per cent if Act and United Future total three seats, subtract 0.8 per cent if they get five and do the same for overhangs. A higher or lower wasted would also change the arithmetic by a percentage point or so.
National has cleared 45 per cent only twice since 1963 - though both times coming out of opposition into government.
If New Zealand First does clear 5 per cent, National's task gets harder - by roughly 2 per cent. National has won 48 per cent only once since 1951.
If National can't get enough votes to govern with Act and United Future, it will need the Maori Party.
It has ruled out New Zealand First and the Greens are likely to rule it out.
Now turn the telescope around. National's huge poll leads over Labour are not as big as they look.
If New Zealand First clears 5 per cent, it would be available to Helen Clark.
If Labour gets 39 per cent, the Greens 5.5 per cent (for seven seats) and Anderton his one seat, Labour would have a working majority without the Maori Party.
If New Zealand First wins no seats, the Maori Party comes into play.
If Labour gets just 38.5 per cent and combines with the Greens (six seats on a 5 per cent party vote) and Anderton (one seat) it would be six seats short of 62.
In theory, the Maori Party could make up the difference and its choice of main party would decide which controls the incoming government.
There are good reasons for the Maori Party to make National king and good reasons to make Labour queen.
But there are better reasons, in Maori Party strategists' eyes, to stay "independent" - to abstain on the Budget and on no-confidence motions, as the Greens have done this term, but also seek a ministerial role.
Who would rule if the Maori Party made no choice? If New Zealand First is not in Parliament, it would come down to which of National/Act/United Future and Labour/Green/Anderton had more seats.
Assuming Act and United Future total four seats and Greens plus Anderton total seven, National would need four seats more than Labour - possible on about 3 per cent more of the party vote.
If a stalemate develops, Helen Clark has one advantage over John Key - incumbency.
She can stay in office until she is voted out even if Labour has fewer votes than National.
Not fair? In 1978 and 1981 National clung to office even though Labour won more votes, thanks to first-past-the-post system quirks. What goes around comes around.
TAIL WAGGING THE DOG
* If Act and United Future get four seats, National would need 58 seats for a majority of 62 - assuming there are two or three overhangs.
* If New Zealand First fails, and the wasted vote is about 5.5 per cent, National would need just under 46 per cent of the party vote to get 58 seats - a voting share it has achieved twice since 1963.
* If New Zealand First clears 5 per cent, National - having ruled out NZ First as a partner - will need about 48 per cent of the party vote. It has collected this share only once since 1951.
* If New Zealand First clears 5 per cent, it would be available to Labour.
* If New Zealand First wins no seats, the Maori Party might come into play.
* If Labour gets 38.5 per cent and combines with the Greens (six seats on a 5 per cent party vote) and Anderton (one seat) it would be six seats short of 62.
* The Maori Party could make up the difference. Its choice would decide which main party led the government.
