Why are you being told to vote on MMP?

Don’t get excited. Simon Power is a measured man. If you want a change from MMP voting, you can’t till 2017. And then it might not be a big change.

The principled reason for a referendum on MMP is that it makes democratic sense to affirm or not the decision made in anger (against radical Labour and radical National) in 1992-93. You have had five elections to try it out and test its governments.

The last time before MMP a different national voting system was tried, it lasted two elections. In 1908 and 1911, in seats where no candidate won 50 per cent of the votes, a runoff ballot was held later.

The Liberal government made the change to overcome split votes within its ranks and with Labour but in fact it didn’t help much and the post-1912 Reform government reinstated one-vote first-past-the-post (FPP) in which the candidate with the most votes wins — as in the electorate seat vote under MMP.

The Liberals’ manoeuvre illustrates National’s second reason for a vote: that under FPP from 1935 to 1993 it scored a higher ratio of seats to votes than Labour and in 1978 and 1981 won office with fewer votes than Labour.

National’s business backers like that because National is friendlier to them than Labour is. Expect them to back change.

But which of Power’s four options will they back?

The preferential vote, in which voters rank candidates in each electorate and losers’ votes are reallocated to the leaders until someone gets 50 per cent, is used in Australia’s federal lower house. It is like the 1908-11 system but there is only one vote.

The single transferable vote (STV), used in Australia’s Senate, Tasmania and Canberra, has multi-MP electorates (in the Senate’s case the electorates are states). Voters rank candidates and losers’ votes are reallocated until the required number of MPs get the necessary quota.

This semi-proportional system appeals to experts and ran second of the four alternatives to FPP in 1992.

FPP’s history poses a problem for anti-MMP campaigners if it is the choice for a runoff referendum in 2014. So thoughtful opponents of MMP lean towards the supplementary member system, luridly initialled SM. John Key is an SM man.

SM, like MMP, is based partly on electorate seats. Like MMP it tops up parties’ electorates haul with MPs from lists. Unlike MMP, the proportional vote is of the list only, not the whole Parliament.

Thus, compared with MMP, SM is kinder to big parties which win lots of electorate seats and, in this Parliament, the Maori party, which would add a list seat to its five electorate seats. National would have an edge over Labour because it needs fewer votes on average for each electorate seat it wins. The Greens and ACT would lose seats and influence.

In 1999, 2002 and 2008, if the votes had been cast in exactly the same way party-by-party as under MMP, SM would have delivered single-party governments.

Moreover, by keeping small parties’ MP counts small (even if not so small as under FPP when for a long period none won seats), SM eases a National fear that small parties in Parliament are more likely over time to support Labour than National. (Hence Key’s vigorous wooing of the Maori party.)

The results would also to some extent depend on the ratio of electorate to list seats. Key wants 90:30 instead of the present 70:50 (actually, in this Parliament 52 list seats because the Maori party won two more electorate seats than its party vote entitled it to.)

Labour would rather keep MMP, even though in 1992-93 Helen Clark was the leading MP in the pro-FPP campaign. But it wants changes.

One is to eliminate the “waiver”, under which a party which wins one electorate seat does not need to get 5 per cent on the party vote for proportionality. Without the “waiver”, ACT would now have one seat, not five. Winston Peters would have been a lone MP in 1999.

The second change is to a 90:30 or 80:40 ratio. The principled reason for this is that the electorates would be smaller and their MPs more accessible. The self-interested reason is that Labour is more likely to win provincial city electorates if they are shorn of surrounding rural areas tacked on to them in MMP’s bigger electorates.

These are among issues Power has said are to be examined if MMP wins in 2011. Another is a lower threshold of 4 per cent. But if voters opt in 2011 for change Labour will push this “enhanced MMP” as the “real” MMP option in 2014.

From this you will be getting a message: that parties see the voting system as theirs, not yours. Power tellingly said “the government” had to make a decision.

Yet voters — you — have worked out how to work the system to get or dismiss governments. The “wasted” vote for parties which don’t get seats was cut to 1.3 per cent by 2005 and a start made in 2008 on reducing number of seated parties by dismissing Peters. After 2014 there will likely be five parties in Parliament, maybe just four.

If so, what will be the point of change? That is for voters — you — to say, not MPs.