Earlier this week, I reported the polling-place correlations of votes for various options in the New Zealand electoral-system referendum of 2011.
An analysis of the split-voting statistics, as compiled by the Electoral Commission, offers another window on the same questions addressed there. The advantage of these data is that they are based on the Commission’s examination of individual ballot papers, as votes in the two parts of the referendum were cast on a common ballot. ((The same page at the Electoral Commission carries out the split-ballot analysis in each district, although not in each polling place.))
As we already knew, most voters who voted to “Keep” MMP (Part A of the ballot) did not vote at all on Part B, where they could select among several potential replacement systems. In fact, 54.7% of “Keep” voters cast “informal” ballots (meaning blank or invalid).
What is most striking is that of those who cast a vote in Part B, a very large plurality voted for the old First Past the Post (FPTP or FPP) system. The percentage of valid Part B votes for FPTP cast by those who voted in Part A to keep MMP was 40.4%! I wonder how many of these were “insincere” votes, by voters who assumed that FPTP could never defeat MMP in the follow-up referendum that would have happened in 2014 if a majority had voted for change in Part A.
The next most popular choice for “keep” voters was STV, with 24.0%. This, of course, makes sense. Voters who prefer proportional representation ought to rank STV and MMP one after the other as their sincerely preferred choices among the systems on offer.
For third place among “keep” voters who chose any system in Part B, “Supplementary Member” actually edged out “Preferential Voting”, 18.7% to 16.9%. The choice here is an interesting one, as it indicates a preference for any sort of mixed-member system–Supplementary Member is actually a mixed-member majoritarian (MMM) system–over a return to all single-seat districts with ranked-choice ballots. (Preferential Vote = Alternative Vote or Instant Runoff.) In terms of sincere voting, it is not straightforward which of these “should be” preferred by voters whose first choice is MMP.
On the one hand, MMM (SM) retains a tier of nationwide proportional seats, but these would cease to be compensatory (and, under the specific proposal, there would have been many fewer of them). On the other hand, while PV (AV) abolishes all party-list seats, it gives voters for a losing party in a district the potential of determining on preferences which of the big parties wins the seat. Both systems would likely produce majority governments frequently, but those majorities and the campaigns that produced them would have been of a different character.
As for the “change” voters, there are no surprises. Only 3.7% did not cast a valid vote in Part B. Of the remaining voters who did cast a valid vote, just under half (49.8%) voted to go back to FPTP, and 28.0% voted for MMM (SM).
In the earlier correlation analysis of polling place results, I noted the lack of correlation between the vote for Part A and the vote for STV. As we saw above, 24.0% of “Keep MMP” voted for STV, and so did 12.4% of the “Change” voters (for whom STV came in third place, ahead of PV/AV). When the informal votes are included in the denominator, the percentages drop to 10.9% and 11.9%, strikingly close. It is not possible to say for sure from the available data, but maybe STV was a Condorcet winner in the wider electorate, albeit not an especially popular one overall. That would make some sense, as it provides the compromise features of all members being elected in local districts, yet offering a considerable degree of proportionality.
In any case, MMP is now clearly confirmed as the New Zealand electoral system, and so discussion shifts to the formal review of MMP, and how the system might be “improved”.