More than a quarter of those who voted gave their electorate vote to someone from a different party than the one they backed for their party vote. Chris McDowall breaks it down.

View Chris McDowall’s incredible interactive mapping every booth’s votes from the 2017 general election here

Last Friday the Electoral Commission released detailed statistics on how New Zealanders voted in the 2017 general election. The website features special vote breakdowns, electoral vote statistics by party, an extended explanation of the Sainte-Laguë allocation formula and more. Be still, my beating heart!

The split vote tables caught my eye. These statistics detail how people split their votes between political parties. The more I looked, the more intrigued I became.

A quick refresher. Under MMP, each voter gets two votes: an electorate vote to choose their local member of parliament and a party vote to decide how many seats each political party gets in parliament. Most people give both votes to the same party. A split vote is when a person votes for an electoral candidate but not his or her party. In the 2017 General Election, 27.3% of voters split their votes — a drop from 31.6% in 2014.

Split voters are fascinating. Political coverage typically sweeps people into political buckets. Commentators tend to talk about broad categories: the National voters, the Labour voters, the Greens and those mysterious “undecideds”. This masks the diversity of the nation’s nuanced and sometimes seemingly contradictory voting behaviour.

Here is a flow diagram of how New Zealanders allocated their electorate and party votes in 2017.

Bars on the left represent how many votes each party received for their electoral candidates (e.g. 137,900 people voted for their local NZ First candidate with their electoral vote). Bars on the right represent how many party votes each party received (e.g. 186,700 people voted NZ First with their party vote). The curved lines connecting the bars show the degree to which people split their votes (e.g. 76,400 people gave two ticks to NZ First, while 44,600 people voted for a Labour candidate with their electoral vote but NZ First with their party vote).

For legibility, only flows of 10,000 votes or greater are displayed. This means that the flows on the graphic don’t sum to equal the bars. Also, the “Other” category includes informal votes.

A few interesting details pop out:

Just 2,400 people gave two ticks to ACT.

Nearly 57,000 people voted for a Labour candidate but cast a party vote for National

Just under 42,000 people voted for a National candidate but gave their party vote to Labour

NZ First drew party votes in roughly even numbers from people who voted for a National or Labour candidate.

TOP also drew most of its party vote support from people who had voted for either a National or Labour candidate, but with a clear leaning toward Labour.

More people cast an electorate vote for a Māori candidate and a party vote for Labour than gave two ticks to the Māori party.

Around 13,000 more people voted for a Green electoral candidate than cast a Green party vote.

Labour and Green party split voters effectively swapped votes as 80,000 people voted for a Green candidate but gave their party vote to Labour, while 84,000 people voted for a Labour candidate but cast a Green party vote.

The overall pattern of split votes is by no means universal. Each electorate has its own distinct patterns. The seven Māori electorates, for example, show markedly different voting behaviours to the global sums.

National, TOP and NZ First did not field candidates in the Māori electorates, yet each received a small boost to their party vote from these voters.

Nearly half of voters who voted for a MANA candidate, cast their party vote for Labour

Similarly, just under half of voters who cast a Green electorate vote, voted Labour for their party vote

Māori party candidates collectively received 44,000 votes across the seven electorates, but only 19,800 party votes.

15,400 people who voted for a Māori electorate candidate cast a party vote for Labour.

The larger voting patterns hide smaller stories. My favourite is perhaps New Zealand’s ultimate protest vote. One person in Epsom chose to give one tick to the Conservative candidate, Leighton Baker, and the other to Aotearoa Legalise Cannabis Party. Smooth move, Cool Breeze. Smooth move.