For softfruit

[ciphergoth]

Another diagram showing the fortunes of the Lib Dems - I had another go to see if I could show more of what's going on.

Again, the position in the diagram (and the percentages) indicate the share of major party vote that each party gets, and the pie charts indicate the proportion of seats that each gets.

Looking at those polls, the Lib Dems had better hope that Clegg is going to completely turn around the fortunes of the party, or they are facing total irrelevance, which is a long way from the bright hopes entertained after the 2005 elections.

Comments

[green-badger.livejournal.com]

Am I missing something? Why are the numbers of seats different if everyone gets the same % of the vote?

[zotz]

Swings affect different parties unequally for two main reasons I'm aware of - firstly, incumbent MPs usually have a personal vote which effectively favours retaining the government, and secondly that the different parties do well in different sorts of seat - if the (say) Lib Dem vote is quite concentrated in specific areas, then piling up extra votes there won't get many more seats. That sort of distribution would be relatively resistant to either rises or falls in national support.

[softfruit.livejournal.com]

That's all true but actually the opposite of what the diagram shows - it's based on "straight swing" while those are the factors (incumbency etc) that mean Paul's chart prediction of 9 Lib Dems on that opinion poll almost certainly underestimates things: people elected in 2001 and 2005 as Lib Dems would gain an incumbency factor and so be less likely to lose their seats.

[zotz]

The Lib Dems were a random example. I don't offhand know what prediction method Paul's using - it must take these factors into account, given the observed asymmetries.

Whether 9 is a plausible figure given the current poll performance is a good question - electoral wipeouts on that scale have certainly happened, although I'm not aware of a British example.

[softfruit.livejournal.com]

The asymmetries are based on the 2005 result; the predictions all are straight 3-way swings, so don't factor in the incumbency factors built up from 2005 to (next GE). Those are hell to calculate anyhow, especially given the boundary changes and unpredictability of which PPCs will be incumbents in areas of the new seats. Arguably they're not the role of a swingometer anyhow - to me after the votes are cast a swingometer should highlight that seat X would have changed hands but for local factors like incumbency.

I'm not sure if he's taking the 2005 results "as they were" or a projection of them onto the new constituencies that the next GE will be fought on, which IIRC shift about ten seats net from Lab to Con.

[zotz]

to me after the votes are cast a swingometer should highlight that seat X would have changed hands but for local factors like incumbency.

Well, the aim should surely to predict an overall outcome, which would mean assuming an overall incumbency effect - in any given seat the question would be whether there's more or less incumbency than average, or indeed a negative effect if the voters have taken against their member.

So what method is actually being used, then?

[ciphergoth.livejournal.com]

The model assumes that the total number of votes cast does not change, that the votes given to all other parties do not change, and that the proportion that a given party achieves in one constituency compared to another doesn’t change.

This isn't quite "straight swing" - uniform swing is mathematically messy with lots of irritating discontinuities. However, I don't suppose it gives radically different results.

[ciphergoth.livejournal.com]

BTW, no, I'm not using new boundaries. Can I download a voting numbers spreadsheet from somewhere which has done this projection, do you know?

[softfruit.livejournal.com]

Take the 1983 general election. Labour and the Alliance (LibDems) got almost the same share of the vote nationwide - 27% and 25% respectively.

Now, as a rule of thumb, you need about 40% of the vote in a constituency to win it and get the MP. Strictly you need 50.1% of course, but if the votes for the other parties are split you just need one more vote than the next most popular.

However, the Alliance vote was evenly distributed - they got about 25% everywhere, which meant a lot of second places (eg Lab 40%, All 25%, Con 25%, Others 10%) while Labour got a lot of 40% type votes in some areas and 10% type votes in others - so a lot of first places and a lot of third places, which average out to 27% but is much more concentrated in particular parts of the country.

Result: 203 Labour MPs, 23 Alliance, for almost the same number of votes.

Similarly, Plaid get hardly any votes at all, but almost all their voters live in four North & West Wales constituencies and so they get 3-4 MPs in most elections.

A dangerous oversimplification...

[hairyears.livejournal.com]

Geographic spread. Getting 10% of the vote in every single seat in the United Kingdom equals zero seats. Getting 33% of the vote, evenly spread across the UK, means winning the tiny fraction of seats where the other two parties are evenly split at 32.9% and some independent candidate loses his deposit without taking your votes... A particular concern when the largest small party are the Greens, who eat disproportionately into the Lib Dem vote.

My point is that the major parties are geographically-concentrated: the Conservatives dominate in suburban constituencies with a golf course, and in most of England's rural seats; Labour dominate in inner-city constituencies and win elections by displacing the Conservatives from suburban seats in Northern England. When they fail to do this, we get a Conservative majority in Parliament.

The Lib-Dems have a presence everywhere but they only have the critical mass of 'core vote' in a small geographical concentration of constituencies in South-Western England - and in Scotland, where the Conservative party have been squeezed out entirely and the election's a three-way contest between Labour, the Lib-Dems, and the Scots Nationalists.

The tiny fraction of three-way marginal seats where the Lib Dems have a significant core vote are 'battleground' seats for the two major parties, too: winning elections is about taking marginals. Needless to say, massive resources are poured into these local contests and predicting results is more of an art than a science.

An affluent inner-city area like Islington would be a good example: Labour and the Conservatives can rely on an 'Ignorant Vote' among the housing projects and the old age pensioners respectively; the election is decided among a tiny fraction of floating voters among the 'chattering classes', most of whom will have been indoctrinated into an unchanging political stance at university and, as adults, live among like-minded friends and will only consume news media that confirm their existing prejudices. Making headway against such entrenched positions is a Sisyphean task, and it may well be that the long-term Lib-Dem strategy will be to expand from it's geographical base rather than waste resources campaigning as a 'third party' in the marginals.

[softfruit.livejournal.com]

SHINY!!!! Thankyou!!

Though of course straight-swing is misleading here: given we got 6 MPs on something like 2% of the vote in the 1950s, the wipeout section of the grid is unlikely to actually play out quite as readily as the simple swing maths suggests. And some would see the ICM poll position as better than the 2005 result given the negotiating power it suggests: enough MPs to be kingmaker rather than facing another 5-year Labour majority government.

Love that midpoint.

[boyofbadgers.livejournal.com]

I think you're right with regards to total wipeout, but it's worth bearing in mind that the Alliance in 1987 and the LDs in 1992 both only won ten seats with 23.8% and 19.2% of the vote respectively.

[softfruit.livejournal.com]

Not quite: in 1987 the tally was 22 (17 Lib, 5 SDP) and 1992 was 20.

[softfruit.livejournal.com]

YOur percentages are a bit skewed there too I think. Are you just going on the MPs in England (where 10 would almost certainly be correct given the tranche of Scottish Liberal seats)?

[boyofbadgers.livejournal.com]

Bugger, you're absolutely right! I thought the numbers were a bit suspect.

[ciphergoth.livejournal.com]

Well my model predicts that if people voted as they did in 2001 then the LDs would have 37 MPs, but in the event they had 52 seats, so I'm starting to think my model needs work.

This has been done before - where is it being written up?

[damerell.livejournal.com]

The one ray of joy is that the Tories get boned for not bringing in PR while they had the chance.

[ciphergoth.livejournal.com]

Sadly, they don't; they get more seats than their proportion of the vote in every plausible scenario.

[paulthegeek.livejournal.com]

Firstly, hi. aster13 pointed me in your direction a while ago and I really enjoy the things you post.

It's true that they get more than their proportion of the vote, but Labour do MUCH better than their proportion of the vote. Based on the ICM results, I'm sure the Conservatives would prefer the largest share in a hung parliament, rather than an equal share with Labour.

As to whether the LibDems (or maybe the Greens) would join them in an coalition... that's a different matter.