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The minimum swing needed in the special votes for the Greens to steal that seat

A 4.6-point swing in specials relative to preliminary, about 0.6 points more than my projection, would get the Greens a 14th seat at National’s expense. But even less might be sufficient.

I think a projection, which I posted yesterday, is more useful information that the “minimum required swing” calculations that I did for the 2011 election. But if anyone is interested in knowing exactly what the Greens need to clear the bar, here is that spreadsheet I did in 2011, updated with 2014 data: Required changes in special votes to steal seats, 2014 election.

I won’t go through all the various possibilities. If you’re curious, feel free to do that yourself using the spreadsheet. The situation that is most interesting, because (other than no change) it’s most likely, is where the Greens would pick up a 14th seat in exchange for National’s 61st (and absolute majority).

The Greens would need to swing +4.60 points in the special votes alone (not total votes), relative to the preliminary count, to take a seat. I have them projected to swing +4.05 points, so this isn’t unrealistic.

Here’s the catch: In the preliminary results, Labour has the 120th quotient and National the 119th. This means that Labour would lose a seat before National. So they need to gain a little to make sure it’s National, not them, who loses the seat. This isn’t hard: they’re 561 votes away (relative to an assumption that specials are distributed identically to preliminary), or +0.19 points. My projection has them well ahead of this.

So the “minimum change required” situation has both Labour and the Greens taking from National. You’ll notice in the table below that the Greens don’t actually need National to lose as much as it did in my projection: -4.79 points, not as much as my projected loss of -5.58 points.

In terms of absolute votes, this is a swing of 1,648 relative to my projection. I said in my last post that 1,129 votes more would suffice. The assumptions behind these figures are different. The projection margin (1,129) assumes that the Greens only gain votes, and no-one loses any, i.e. it’s likely to be an overestimate (not by double though—the equivalent National loss is 5,058). The “minimum required” swing (1,648 relative to projection) assumes that all other parties perform in the specials identically to the preliminary result. Historically (and hence in my projection) most left-wing parties do better in the specials at National’s expense, and these help the Greens too. So this is also likely to be an overestimate, probably more so.

So really, the most important hope for the Greens to hang on to is that they will perform about 0.6 points, or maybe (depending on what else happens) even just 0.35 points, better in the special votes than the 2011 swings might imply.* As I said in my last post, it’s certainly possible, but it’ll be very close. If I were Steffan Browning or Maureen Pugh, I’d have a very nervous two weeks ahead.

Party Preliminary Projection Special required Change on prelim Change on projection Total required Change on prelim
National 48.06% 42.48% < 43.26% -4.79% +0.79% < 47.47% -0.59%
Labour 24.69% 28.10% > 24.88% +0.19% -3.22% > 24.71% +0.02%
Green 10.02% 14.07% > 14.63% +4.60% +0.56% > 10.59% +0.57%

* My projection applies the 2011 preliminary-to-special swings multiplicatively, not additively, to the 2014 preliminary result. A full method description is in the post describing the projection.

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