September 13, 2017

Thresholds and discards, again

There are competing explanations out there about what happens to votes for a party that doesn’t reach the 5%/1 electorate threshold.  This post is about why I don’t like one of them.

People will say (such as on NZ Morning Report this morning) that your votes are reallocated to other parties.  In some voting systems, such as the STV we use for local government elections, reallocating votes is a thing. Your voting paper literally (or virtually) starts off in one party’s pile and is moved to a different party’s pile.

That’s not what happens with the party votes for Parliament.  If the Greens don’t make 5%, party votes for the Greens are not used in allocating List seats.  It’s exactly as if those voters hadn’t cast a party vote, which I think is a simple enough explanation to use.

Now, in the vast majority of cases the result will be the same as if the votes had been reallocated in proportion — unless something weird like a tie happens at some stage in the counting — but one of the explanations is what happens and the other one isn’t.

If you think the two explanations convey the same meaning, you shouldn’t object to using the one that’s actually correct. And if you think they convey different meanings, you definitely shouldn’t object to using the one that’s actually correct.

 

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Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »

Comments

  • avatar
    Savannah Post

    I think the reality though is that the first explanation, the one that is mostly used in the media, is easily understood by the general public whereas the alternative is not. If you only tell people that “it’s exactly as if those voters hadn’t cast a vote”, then they won’t necessarily understand what the effect of that is on the outcome of the election. Explaining it instead as a reallocation of the votes is easier to understand, in my opinion at least.

    1 week ago Reply

    • avatar
      Thomas Lumley

      But why is that easier to understand?

      We know lots of people don’t vote, and it’s not hard to understand that getting them to vote would change things. No-one seems to be mystified as to why get-out-the-vote campaigns are done. I just don’t believe people are confused about what happens to their vote if they stay home and don’t cast it.

      1 week ago Reply

  • avatar
    Leon Iusitini

    And presumably some of the voters who voted for parties that didn’t reach the threshold would object to the idea that their party vote was ostensibly ‘reallocated’ to a different party or parties, especially ones they dislike.

    1 week ago Reply

  • avatar

    Agree! I was enraged when I heard the RNZ reporter talk about reallocation. They should know better. The reason that this is “easily understood by the general public” doesn’t wash with me, and insults all of us. I’m interested in your observation Thomas that in the “vast majority of cases the result will be the same”. What if one party is hovering near 5%, slips below on the night and those votes are not counted – a case of a losing party raises all votes – and if this is the only party to miss out narrowly and they were at a specific end of the political spectrum, then surely the other end of the spectrum will benefit, if only marginally? While this seems hypothetical, this is where the Greens find themselves and this election could depend on a marginal difference. My statistical skills don’t run to the kind of modelling to support my argument but I wonder if anyone more skilled could prove me wrong.

    1 week ago Reply

    • avatar
      Thomas Lumley

      I think the only differences in outcome between the ‘reallocation’ story and the actual algorithm happen when you have exact ties, which probably wouldn’t stay exact after reallocating the votes.

      1 week ago Reply

  • avatar
    Nick Iversen

    What do the rules say about the situation where every party scores 4.9%?

    Not very likely – it would require at least 21 parties. But still a theoretical possibility.

    1 week ago Reply

    • avatar
      Thomas Lumley

      I don’t know. It seems that the Electoral Commission would be unable to comply with Section 191 of the Electoral Act. http://www.legislation.govt.nz/act/public/1993/0087/122.0/DLM310034.html

      I think the right answer would be no-one elected from the lists, but I don’t think that’s what the Act actually says.

      1 week ago Reply

      • avatar
        Alasdair Noble

        But the 60 electorate members would presumably have come from some of these parties (unless they were all independents) in which case the 4.9% from those parties represented by an electorate MP would be counted and the 60 list MP’s divided equally between the parties with at least one electorate MP.

        4 days ago Reply

        • avatar
          Thomas Lumley

          They could all have been independents or all have been from parties that for one reason or another weren’t competing for the party vote. I’m not saying this is *likely*, or *practically important* just that it’s a minor bug in the Electoral Act. Like the Act’s incorrect implementation of the Wichmann-Hill pseudorandom number generator.

          4 days ago

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