Donald Trump has been citing Brexit as the model of how he could win the election despite expections, his surrogates of how there might be a shy Trump vote, like Brexit. So what, if any, lessons can we learn about the US election from recent polling experience in Britain?

In 2015 the British polls got the general election wrong. Every company had Labour and Conservative pretty much neck-and-neck, when in reality the Conservatives won by seven points. In contrast, the opinion polls as a whole were not wrong on Brexit, or at least, they were not all that wrong. Throughout the referendum campaign polls conducted by telephone generally showed Remain ahead, but polls conducted online generally showed a very tight race. Most of the online polls towards the end of the campaign showed Leave ahead, and polls by TNS and Opinium showed Leave ahead in their final eve-of-referendum polls.

That’s the first point that the parallel falls down – Brexit wasn’t a surprise because the polls were wrong. The polls were showing a race that was neck-and-neck. It was a surprise because people hadn’t believed or paid attention to that polling evidence. The media expected Remain would win, took polls showing Remain ahead more seriously and a false narrative built up that the telephone polls were more accurately reflecting the race when in the event, those online polls showing leave ahead were right. This is not the case in the US – the media don’t think Trump will lose because they are downplaying inconvenient polling evidence, they think Trump will lose because of the polling evidence consistently shows that.

In the 2015 general election however the British polls really were wrong, and while some of the polls got Brexit right, some did indeed show solid Leave victories. Do either of those have any relevance for Trump?

The first claim is the case of shy voters. Much as 1948 is the famous examples of polling failure in the US, in this country 1992 was the famous mistake, and was put down to “Shy Tories”. That is, people who intended to vote Conservative, but were unwilling to admit it to pollsters. Shy voters are extremely difficult to diagnose. If people lie to pollsters about how they’ll vote before the election but tell the truth afterwards, then it is impossible to distinguish “shy voters” from people changing their minds (in the case of recent British polls, this does not appear to be the case. In both the 2015 election and the 2016 EU referendum recontact surveys found no significant movement towards the Conservatives or towards Leave). Alternatively, if people are consistent in lying to pollsters about their intentions beforehand and lying about how they voted afterwards, it’s impossible to catch them out.

The one indirect way of diagnosing shy voters is to compare the answers given to surveys using live interviewers, and surveys conducted online (or in the US, using robocalls – something that isn’t regularly done in the UK). If people are reluctant to admit to voting a certain way, they should be less embarrassed when it isn’t an actual human being doing the interviewing. In the UK the inquiry used this approach to rule out “shy Tories” as a cause of the 2015 polling error (online polls did not have a higher level of Tory support than phone polls).

In the US election there does appear to be some prima facie evidence of “Shy Trumpers”* – online polls and robopolls have tended to produce better figures for Donald Trump than polls conducted by a human interviewer. However, when this same difference was evident during the primary season the polls without a live interviewer were not consistently more accurate (and besides, even polls conducted without a human interviewer still have Clinton reliably ahead).

The more interesting issue is sample error. It is wrong to read directly across from Brexit to Trump – while there are superficial similarities, these are different countries, very different sorts of elections, in different party systems and traditions. There will be many different drivers of support. To my mind the interesting similarity though is the demographics – the type of people who vote for Trump and voted for Brexit.

Going back to the British general election of 2015, the inquiry afterwards identified sampling error as the cause of the polling error: the sort of people who were able to be contacted by phone and agreed to take part, and the sort of people who joined online panels were unrepresentative in a way that weights and quotas were not then correcting. While the inquiry didn’t specify how the samples were wrong, my own view (and one that is shared by some other pollsters) is that the root cause was that polling samples were too engaged, too political, too educated. We disproportionately got politically-aware graduates, the sort of people who follow politics in the media and understand what is going on. We don’t get enough of the poorly educated who pay little attention to politics. Since then several British companies have adopted extra weights and quotas by education level and level of interest in politics.

The relevance for Brexit polling is that there was a strong correlation between educational qualification and how people voted. Even within age cohorts, graduates were more likely to vote to Remain, people with few or no educational qualifications were more likely to vote to Leave. People with a low level of interest in politics were also more likely to vote to Leave. These continuing sampling issues may well have contributed to some of those pollsters who did it wrong in June.

One thing that Brexit does have in common with Trump is those demographics. Trump’s support is much greater among those without a college degree. I suspect if you asked you’d find it was greater among those people who don’t normally pay much attention to politics. In the UK those are groups who we’ve had difficulty in properly representing in polling samples – if US pollsters have similar issues, then there is a potential source for error. College degree seems to be a relatively standard demographic in US polling, so I assume that is correct already. How much interest people have in politics is more nebulous, less easy to measure or control.

In Britain the root cause of polling mishaps in 2015 (and for some, but not all, companies in 2016) seems to be that the declining pool of people still willing to take part in polls under-represented certain groups, and that those groups were less likely to vote for Labour, more likely to vote for Brexit. If (and it’s a huge if – I am only reporting the British experience, not passing judgement on American polls) the sort of people who American pollsters struggle to reach in these days of declining response rates are more likely to vote for Trump, then they may experience similar problems.

Those thinking that the sort of error that affected British polls could happen in the US are indeed correct… but could happen is not the same as is happening. Saying something is possible is a long way from there being any evidence that is actually is happening. Some of the British polls got Brexit wrong, and Trump is a little bit Brexity, therefore the polls are wrong really doesn’t carry water.


*This has no place in a sensible article about polling methodology, but I feel I should point out to US readers that in British schoolboy slang when I was a kid – and possibly still today – to Trump is to fart. “Shy Trump” sounds like it should refer to surreptitiously breaking wind and denying it.

Over the last year couple of years Labour’s lead has gradually been whittled away, from ten points in 2012 they are now holding onto only the very narrowest of leads, with many polls showing them neck and neck. At the same time we have seen UKIP’s support getting ever higher, with polls regularly putting them in the mid teens. One naive assumption could be that supporters have moved directly from Labour to UKIP, but in reality there is a lot of churn back and forth between parties. A political party could be picking up support from one group of voters, but losing an equal number of voters somewhere else. The voters now backing UKIP could be people who earlier in the Parliament were backing Labour, even if they didn’t vote Labour in 2010.

Every month YouGov carry out around twenty polls for the Sun and the Sunday Times. In any individual poll the crossbreaks of 2010 Conservative, Labour and Liberal Democrat voters are too small to be robust, but by aggregrating up the polls from a whole month we have enough responses to really examine the underlying churn, and by comparing the figures from 2012 and 2013 to today, we can see how party support has changed.

All these charts are based on YouGov’s figures. For simplicities sake the movement between the parties are always *net* figures – for example, there are a very small number of people who voted Labour last time but said they’d vote Lib Dem this time, but the vast bulk of the movement is in the opposite direction. I’ve netted them up to get the overall movement between each party. I’ve also excluded very small movements made up of less than 0.2%. The percentages are of the whole of the sample, not of each parties support, and because the sample also includes people who say don’t know or won’t vote things don’t add up to 100%. You can click on each image to get a bigger, readable version. With that in mind…


Here’s October 2012, a high point for Labour when they were enjoying an average lead of around 10 points in YouGov’s national polls. Labour’s vote at the time was very robust, they were making a very small net loss to UKIP, but otherwise their vote from 2010 was solid and they had added to it small amounts of support from 2010 non-voters and Conservatives and a large chunk of former Liberal Democrats. Lib Dem support had already slumped, with the large majority of their support going to either Labour or to Don’t know/Would not vote (DK/WNV). The Conservatives had started to lose support to UKIP, but it wasn’t yet a flood – they were also losing some support to Labour and a large chunk to DK/WNV.


Moving onto October 2013, Labour’s lead had now fallen to around 6 points in YouGov’s national polls. They were still holding onto their 2010 support, but their gains from the Conservatives and non-voters were starting to falter. The movement of support from the Conservatives to UKIP had vastly increased, but part of this was balanced out by fewer Con-to-DK/WNV and Con-to-Lab switchers. The number of lost Tories was growing, but lost Tories were also switching their destination, saying they’d support UKIP rather than saying Labour or don’t know. The Liberal Democrats and Labour were also starting to see increased movement to UKIP, though at this point the big chunk of LD-to-Lab voters remained solid.


Finally here is the picture from October 2014. Labour’s average lead in YouGov’s polls last month was just 1.5 points and their retained support from 2010 is now faltering. In 2012 20.6% of our polls were made up of people who had voted Labour in 2010 and would do so again, that has now dropped to 16.6%. Those 2010 Labour voters are now flaking away towards UKIP, the Greens and the SNP. Movement from Con-to-Lab has now dried up completely. The chunk of CON-to-UKIP voters has continued to grow, but mostly at the expense of CON-to-DK/WNV, meaning Tory support has remained largely unchanged. Most importantly that solid block of LAB>LD switchers has started to wither, down from 6.6% of the sample to 4.6%. The Liberal Democrats themselves aren’t doing any better, but their former supporters are scattering more widely, moving to the Tories, UKIP and Greens.

Comparing the churn from 2012 and now you can see Labour’s issue. In 2012 all arrows pointed to Labour, they were picking up support from everywhere and holding on to what they had. Today they still have the benefit of a strong transfer from the Liberal Democrats (though even that’s declining), but they are leaking support in every direction – to the Greens, to UKIP and to the SNP.

One of the reasons the Conservatives ended up falling short at the last election was that they failed to clearly identify themselves as THE party for change – the public wanted rid of Gordon Brown and Labour, but following the debates Nick Clegg managed to make many people think the Liberal Democrats were the more convincing alternative. Ed Miliband may face a similar problem, the government still isn’t popular and still has a relatively low level of support, but the anti-government vote seems to be fracturing away from Labour to alternative non-Conservative parties like UKIP, the Greens and the SNP.

(This post is also featured on the New Statesman’s May 2015 here)


Final lap

A year to go until the general election, meaning there are awful lot of “year to go till the election” posts out there (though two new things certainly worth looking at are the new British Election Study site here and the Polling Observatory’s new election prediction here. The election prediction by Rob Ford, Will Jennings, Mark Pickup and Christopher Wlezien takes a similar approach to Stephen Fisher’s, which I’ve discussed here before, in averaging current polls and then assuming that they move in the same way over the next 12 months as they have done in the final year of previous Parliaments. Unlike Steve’s projection, which has a Tory lead, Ford et al predict a miniscule (0.4%) Labour lead. The difference between the two projections are small, and technical – Ford et al assume a regression towards the long term average, I think Steve assumes a regression towards the previous election result, the inputs are slightly different (the Polling Observatory ones corrects for errors at the last election, my average which Steve uses doesn’t – largest effect of that will be that Steve predicts a higher Lib Dem score) and there are different smoothing effects in there. Expect more predictions along these lines to pop out of the woodwork in the year ahead.

Anyway, I’ve previously written about what I think are the big five concepts that will decide the election – how the improving economy impacts on voting intentions (especially if or as wages start to rise above inflation)? Whether Ed Miliband’s mediocre opinion poll ratings will increase in salience closer to the election, given they aren’t currently prevening a Labour lead? If and how quickly UKIP support subsides following the European elections? To what degree, if at all, Lib Dem incumbents can resist the tide against them? And, of course, what happens in the Scottish independence referendum? So for today, I’m instead looking at the timetable for the year ahead. These are essentially the “known unknowns” – the things that will happen before the next election but which we don’t yet know the impact of, as opposed to all those unpredictable events that will also happen.

25 MAY 2014. European election results. The last set of mid-term elections and the beginning of the final lap. Barring any big suprises UKIP will come top or almost top, the media will go into another Farage frenzy for a couple of weeks and UKIP will enjoy a big spike in the Westminster opinion polls. Do not be surprised to see them at 20% or more in some polls. The question then becomes one of how much of that support is retained over the next eleven months. Also watch how the other parties react, will the Conservative backbenches panic, will the leadership be tempted to ape UKIP? I expected them to go all ferrets-in-a-sack after UKIP did well in the local elections last year, but they held it together surprisingly well. If the Lib Dems do incredibly badly keep an eye on them too – they have been incredibly disciplined as they march towards the guns so far.

5 JUNE 2014. Newark – coming shortly after the European elections we have the Newark by-election. The Conservatives have a fairly chunky majority, it’s not ideal territory for UKIP and they’ve picked a candidate who plays to UKIP stereotypes rather than challenging them like Diane James did in Eastleigh, but the timing means UKIP will likely still be enjoying a big boost.

JUNE 2014. The Queens Speech and the Private Members Ballot – the final session of a Parliament won’t have many exciting bills left, watch who wins the private members ballot though. If a compliant enough Conservative comes top of the ballot then they’ll re-introduce the EU Referendum Bill that got lost in the Lords last time, and if it passes the Commons unamended again the Parliament Act would come into play. Labour and the Liberal Democrats may have to act to kill it in the Commons this time round. The Conservatives will hope a second try at the referendum bill will help win back UKIP supporters, a less charitable interpretation would be that it will offer the Conservatives an exciting opportunity to bang on about a subject normal voters don’t much care about every Friday for six months.

JULY 2014? Summer reshuffle – David Cameron has at least one big reshuffle before the general election (two if the coalition is brought to a formal end at some point), which will be his opportunity to put in place the team he wants for the general election. Cameron’s nature so far has been to avoid lots of changes and it’s rare for a reshuffle to be drastic enough to entrude upon public opinion, but it will determine who some of the big players are.

18 SEPT 2014 Scottish referendum – this is by far the biggest known unknown still facing us. If there is a NO vote (and while the trend has been towards YES, all the polls in the campaign have shown NO ahead) then it will at least have a substantial political impact in Scotland. In the event there is a YES vote absolutely everything would change. There would be a question mark over whether David Cameron should resign, certainly the political agenda would instantly be dominated by questions about the Scottish independence negotiations and the 2015 election would be fought in the knowledge that 40 odd Labour MPs would be elected for a period of only a year.

21 SEPT 2014 – Conference season. This is one of the few fixed, big events of the year that has the potential to impact on public opinion. The dates are a bit mixed up this year – normally the order goes Lib Dems, Labour, Conservatives. Because of the normal dates would have clashed with the Scottish refernedum the Liberal Democrats have moved their conference to last, so it will go Lab, Con, LD. All three will be a showcase for the general election, people will be paying more attention as the election approaches and expect an up-and-down in the polls as each party gets its chance in the spotlight.

OCTOBER 2014? New EU Commissioner – not something that will be noticed by the general public, but does have the opportunity to precipitate a by-election if a sitting MP is sent off to Europe as the new British EU Commissioner. It might even precipitate….

DATE TBC. Boris makes his mind up – we don’t know when it will happen, but at some point or other Boris Johnson will either stand for Parliament, or rule out the possibility of standing at the next election (even if that’s at close of nominations… though I expect the Conservative party will want to shut it down one way or the other long before that). Given it’s Boris it will attract public attention, how the Conservative party manage any return to Parliament will determine if they can use Boris in a role that helps them or if it’s seem only as a first shot in a leadership campaign.

DEC 2014. Autumn statement – presumably any big changes will be in the budget, but if the economic news is positive by the Autumn it’s a chance for George Osborne to highlight it.

DATE TBC. The end of the coalition – at some point the coalition between the Liberal Democrats and the Conservatives has to end or, at least, it needs to be become clear how it will end. The three obvious possiblities are a disordered breakdown over some issue, resulting in a minority Tory government, disengaging to supply and demand for the final few months, or remaining in coalition right to polling day. I suspect the first one won’t happen now, that leaves us an ordered break up with the Lib Dem ministers resigning but continuing to support the government in matters of confidence, or remaining in office right till the end. Even in the latter case, in order to effectively fight an election at some point the Lib Dems will need to appoint spokespeople in areas where they don’t have cabinet ministers and announce policies different to those of the coalition government. How will that impact on Lib Dem support?

JAN 2015. The long campaign begins – it many ways its begun already, or will begin after the Euros or after conference season. It’s a matter of perception, but Christmas is the last real break before the election and at their return in the New Year we will likely see a slew of announcements and policies, the start of the real campaign, and in my view the time when the polls start to come into focus and start to resemble the final result. Don’t get me wrong – there will still be time for things to change, there will still be a budget, manifestos, announcements and possibly debates, but the clock is ticking.

MAR 2015?. The Budget. Budgets are often seen as an opportunity for governments to win support by handing out election bribes. As I write here every year, in recent budgets that really doesn’t seem to have been the result – it’s more common for bad budgets to damage support than good ones to win support. Still, it will be an opportunity for Osborne to give away something to try and win votes, or at least try and portray himself as a reliable safe pair of hands that the country will want to re-elect.

30 MAR 2015. Parliament dissolved.

APR 2015?. The Leaders debates. How much impact they had last time is still debated (did they genuinely increase Lib Dem support, or was it all froth? Did the opportunity cost of the debates dominating the campaign prevent other changes in public support?), but they certainly have the potential to make a difference. We obviously don’t know what the format will be, when they will happen, who they will involve or even if they’ll happen (the genie can go back in the bottle – after the famous JFK v Nixon debate in 1960 there wasn’t another one till 1976) – much of the briefing now by Labour and the Conservatives is probably largely grandstanding and negotiating stances, partly aimed at showing willing so they can paint it as the “other side’s fault” if they don’t go ahead. I wouldn’t expect any debates to have as big an impact as in 2010 because they aren’t “new” anymore – the exception would be if somehow they other parties did agree to Nigel Farage taking part. For a smaller party what happens at the debate is not as important as the credibility brought by being part of the debate to begin with.

7 MAY 2015 – Election Day

As you might imagine, a year out from a general election the one question I get asked more than any other is “well, who is going win then?”. It’s a question I try to avoid answering like the plague. The simple answer is we don’t know – polls measure public opinion now, not a year ahead. Assuming no change from the polls now (which would imply a Labour majority) is a naive approach that would have served you poorly in past Parliaments. Assuming public opinion will change in the same way as it has towards the end of previous elections gives you a prediction (hung Parliament, Tories the biggest party), but also gives you huge confidence margins that stretch from a Tory landslide to a comfortable Labour majority.

My answer, therefore, tends to be to give the five questions (and one observation) that I think will decide the next election one way or another…

1) How will the growing economy effect the polls?

The economy has universally been the issue that voters see as most important in polls since the economic crisis began, and as such has been a major influence on voting intention. Economic confidence amongst the general public started rising sharply early in 2013 in all the major trackers, and has continued on a broadly positive trend. This has coincided with movement in public attitudes towards the government’s economic policies. From being neck-and-neck with Labour on the economy last year the Conservatives now have a consistent lead. Last year YouGov’s cuts trackers consistently showed that people thought that their cuts to public spending, while necessary, were actually bad for the economy, now they show more people think the cuts were good for the economy. It is impossible to draw a causal link, but over the same period the average Labour lead has dropped from about 10 points to around about 5 or 6 points.

Whether or not the facts back them up (that is a discussion for some economic blog elsewhere), the recovering economy seems to be having the effect of convincing some the public that the government’s economy policy was right and that the Conservatives can be trusted more on the economy. I am not an economist and this is not an economics blog, so I have no educated view on if the economy will continue to grow, which seems to be what commentators expect. Assuming it does, will that lead to continuing increases in government approval and a bigger lead for them on the economy, and will that translate into increased support? More specifically, while polls show people are more optimistic about the economy as a whole, they are still downbeat about their own personal finances. Will people themselves start to feel better off in the next 14 months, and would that translate into more government support?

A final thing to watch there is how important people say the economy is. There are examples of government’s losing elections despite being ahead on the economy – the classic is 1997. The reason becomes apparent if you look at what issues people told pollsters were important in 1997 – it wasn’t the economy (where the Tories were still holding their own), it was public services like the NHS and education where Labour were a mile ahead. I don’t think 14 months is long enough for this to happen, but if the economy really starts getting better keep an eye on whether people stop telling pollsters it is such an important issue.

2) Will Ed Miliband’s unpopularity matter anymore than it does now?

I find the contrast between Ed Miliband’s ratings and Labour’s support a puzzle. There really is a gulf between them. The basic facts are straightfoward – for an opposition leader whose party has been consistently ahead in the polls for years Ed Miliband’s ratings are horrible. His approval ratings are horrid, down at IDS, Howard and Hague levels; best Prime Minister ratings normally track voting intention pretty closely but Ed Miliband trails behind David Cameron by around 15 points. Polls consistently find that people think Ed Miliband is weak and not up to the job of Prime Minister. This is not just a case of opposition leaders always polling poorly compared to incumbent Prime Ministers – if you compare Ed Miliband’s ratings now to David Cameron’s in opposition Miliband is doing far worse. For example, in 2008 49% thought David Cameron looked like a PM in waiting, only 19% think the same about Ed Miliband now. To claim that Miliband’s ratings are not dire is simply denial. Yet Labour consistently lead in the polls.

Pause for a second, and imagine that we didn’t ask voting intention in polls. Imagine all you had to go on was all the other figures – the polls asking who people would trust more on the economy, who would make the better Prime Minister, who people trust on the issues they currently think are most important. Based on those figures alone the next election looks as if it should be a Conservative walkover…and yet Labour consistently lead in the polls.

The paradox between the underlying figures, which in most areas are increasingly favourable to the Conservatives, and the headline figures, consistently favourable to Labour, are fascinating. They are something I’ve returned to time and again without apology, as I’m sure there’s a key message here. Whatever the result of the next election, it’ll tell the loser something very important. If the Conservatives win, Labour will need to learn about using the goodwill an opposition gets to actually build up the foundations to, well, support their support (I suspect they’d also have to accept that getting a leader who people take seriously as a potential PM really is a prerequisite). If Labour win, the Conservatives should take home the message that leadership, economic competence and being preferred on policies really isn’t enough, that they have a serious issue with how people perceive their party and its values that needs to be addressed (I doubt they would learn that lesson, but there goes).

Given Labour are ahead now, I think the question is whether perceptions of the opposition and the choice of Prime Minister increase in importance as the election approaches and voting intention becomes less of a way of people indicating their opinion of the government, and more a choice between two alternatives. The reason Labour poll badly on so many of these underlying questions is not because Labour voters say they prefer Cameron and the Tories, it’s because many Labour voters simply say don’t know (or none of them). They aren’t convinced Miliband would be a good PM or Labour would run the economy well. Will those people overcome those doubts? Vote Labour regardless? Or do something else?

3) What level of support will UKIP get at the general election

Looking back over UKIP’s performance in the Parliament so far their support has mostly followed a pattern of election successes leading to boosts in the polls, followed by a decline to a new, higher plateau. I think UKIP can fairly comfortably expect a strong performance European elections (personally I would still expect them to come top, but whatever happens it’s going to be a strong showing). This will in turn be followed by another publicity boost and another boost in the Westminster polls. It will vary between different pollsters, as ever, but I think we can expect UKIP in the mid to high teens with the telephone polls and up in the low-twenties with the more favourable online companies.

From then on, it’s probably a case of a decline as we head towards the general election as the focus moves more towards the Con-v-Lab battle. The question is how quickly that support fades and to what extent. Here we are very much in unknown territory. UKIP got up to around 8% in the Westminster polls following the 2009 European elections, but declined to around 3% by the 2010 election; the Greens got up to 8% in the polls following the 1989 European election, but declines to 0.5% of the vote by the 1992 election. This time round is clearly different in terms of the size and scale of UKIP’s support and history provides no good guide. Neither does present polling – people are notoriously bad at answering questions on whether they’ll change their mind or what might make them change their mind. We are flying blind – but given that UKIP support has thus far disproportionately come from people who supported the Conservatives at the last election it is something that would have implications for the level of Tory support come the general election.

4) How resilient will Liberal Democrat incumbents be?

The three points so far have been about levels of overall support at the next election. The fourth is instead about distribution of the vote and therefore the outcome in numbers of MPs. On a uniform swing the Liberal Democrats will face severe losses in the election. It obviously depends just how badly they do, whether they are still in the coalition, whether they recover towards the election and so on, but projections of them losing half their seats are not unusual. However, there is also an expectation that Liberal Democrats will do better than this because of their incumbent MPs’ personal vote. Analysis from past elections and from studies like the PoliticsHome and Lord Ashcroft polls of marginal seats are pretty consistent in showing that Liberal Democrat MPs benefit more from personal votes than politicians from other parties, they handily won the Eastleigh by-election and have managed to hold on to councillors in some (but not all) of the areas where they have MPs. This would point to the Liberal Democrats actually doing better in terms of MPs than the raw numbers would suggest, although don’t expect magic… Lib Dem MPs might outperform the national trend, but it doesn’t render them immune to it. If you’ve lost a third to a half of your support, it has to come from somewhere and would be naive to expect it all to come from places you don’t need it.

As a caveat to this Lib Dem optimism though, look at the Scottish Parliament election in 2011. In that case Lib Dem incumbents didn’t seem to do any better, if anything the Liberal Democrats lost more support in areas where they had the most support to begin with, the very opposite pattern. The cause of this is probably a floor effect (the Lib Dems lost 8% of the vote in the election, but started off with less than 8% in many seats, so by definition more of their lost support had to come in their stronger seats). If the Lib Dems do really badly we may see the same effect at Westminster, if the Lib Dems lose enough support it’s impossible for it all to come from seats where they have hardly any support to begin with! The question is to what degree, if any, Lib Dem MPs can outperform the swing against them.

5) Will Scotland be voting?

Or perhaps more accurately, will the Scottish MPs be sticking around afterwards! All the polls on the Scottish referendum so far have shown the NO campaign in the lead. There has been a slight trend in the direction of yes, but nothing more than that. Personally I would expect the NO campaign to win, but there is obviously a chance they won’t and if so it would massively change our predictions for the next election. Exactly how and when Scottish MPs cease to be members of the House of Commons would need to be decided, but it would obviously disproportionately affect Labour – the Conservatives have only one Scottish MP to lose. More important though would be the wider effect on politics, thus far the Scottish independence referendum is something that has had minimal effect upon politics south of the border. Until January the London based media barely even mentioned it, it’s still something that’s very much a sideshow. If Scotland were to vote yes then then the negotiations in the following 18 months would suddenly become an issue of paramount importance, David Cameron’s position would presumably come under some pressure but either way, nothing would be the same anymore. I don’t expect it to happen, but it would be remiss of me not to include it here.

So, five things that I think will decide the election. I said there was an observation too – remember the impact of the electoral system. This one isn’t a question, we know that the system is more helpful to Labour than the Conservatives and, given the government’s failure to get the boundary review through, will remain that way. Getting ahead in the polls is not enough for the Conservatives – it would probably leave Labour as still the largest party. To get an overall majority the Conservatives need a lead of somewhere in the region of 7 points. We can’t be certain of the exact figures (the double incumbency bonus of MPs newly elected last time round will shift things a bit), but we can be confident that just being ahead isn’t enough for the Tories – they need to be well ahead.

Over on the right hand side of this site is a projection of how the current polls would translate into seats at a general election tomorrow, if there was a uniform swing. On twitter and suchlike I sometimes see if referred to as UKPR’s current prediction, but I’m afraid it isn’t. Polls don’t predict the next election, they measure support now, so the polling average here isn’t my best guess for the shares of the vote at the next election, it’s a measure of support in an election tomorrow. Of course, there isn’t an election tomorrow, and if there was, the polls probably wouldn’t be as they are – if there really was an election tomorrow then the last three weeks would have been full of manifestos, policy announces, campaigns and debates which may or may not have had some impact.

It’s also worth noting that while uniform national swing is not a bad guide by any means, it can certainly be bettered. To start with it’s definitely worth dealing with Scotland seperately based on Scottish polling figures, it might also be useful to include some assumptions about incumbency effects in seats with new MPs, and some degree of random variation at the margins.

I deliberately don’t make predictions this far out, given the huge amounts of unknowns. I tend to find most people who do predict this far out with any degree of confidence are – probably unconsciously – merely predicting what they would like to be the case. It’s rare to find someone confidently predicting a Labour victory who wouldn’t like a Labour victory (or who has an ideological axe to grind against the Tory leadership), or vice-versa on the Conservative side. Given the prominence of Nate Silver and other election prediction sites at the last US election I would expect a plethora of more academic and sensible election prediction models come the actual election (hell, I know for certain of several groups of academics working on various models), but so far virtually the only prediction I have seen that moves beyond wish-fulfillment to actually come up with a poll-based model is the attempt by Steve Fisher at Oxford here, with an explanation of the model here.

Steve’s model is a simple one – it is purely based upon voting intention polls and how they have tended to relate to the election result that follows*. We cannot assume that the polls will remain unchanged in the run up to the next election, given that in past Parliaments they have tended to change. Past change has not been a random walk, with equal likelihood of government’s gaining or losing in the polls – this is the key to Steve’s model. In the past the polls have rended to regress towards the result of the previous election (usually in the form of the government recovering). What Steve has done therefore is to take the current polls, and then factor in the sort of size and scale of changes that have typically happened to the polls over the last years of previous Parliaments, then based a prediction on that. At past elections this would have proven to be a more accurate predictor than just taking the current polls. That is not to say that that it is a particularly accurate prediction, only that in the past it would have been more accurate than assuming no change.

On that basis, if the polls over the next year behave like the polls in the last year of previous Parliaments the most likely result come the general election is a Conservative lead of 5 points over Labour, which would produce a hung Parliament with the Conservatives the largest party. The most important word in that sentence is probably the “if”, and perhaps the most important thing to note in Steve’s projection are the large prediction intervals around it. Steve’s model predicts the Conservative vote will be 37%, plus or minus 8.5 (so between 29% and 46%), the Labour vote at 32%, plus or minus 6.4 (so between 26 and 39). These are huge gaps. Of course, results towards the centre of those ranges are still considered more likely, but it underlines the imprecision of the projection, and the limitations on using current polling data to predict a general election a year away. Polls a year out from the election are not a very good prediction of the election. It would be wrong to say that anything could happen (Steve’s model, for example, suggests it is unlikely that Labour would get over 40, or that the Conservatives would fall below 29), but certainly a lot of different outcomes could happen.

It also reflects the sheer variety of elections. One criticism I’ve seen of Steve’s model is that this election will be different because of the coalition, the UKIP factor and the realignment of the Lib Dem vote. That may very well be true, but we could say the same about other elections – 1964 had two late changes of leader, 1966 wasn’t a whole term, 1974 was different because the Liberals started contesting all seats, 1979 was different because of the Lib-Lab pact, or the winter of discontent, 1983 was different because of the Falklands and the SDP split, 1992 was different because of Thatcher’s removal, 1997 was different because of the sheer scale of the landslide. 2001 was different because Labour never really had any mid-term blues to come back from. The infrequency of elections means that almost by definition each one has things that make it unique and different – yet Steve’s out-of-sample predictions shows the model would been a better tool at predicting those past elections from 20, 12 or 6 months out than just looking at what the polls 20, 12 or 6 months out were saying (it also underlines the difficulty for political scientists in coming up with any decent models at all – you only get 16 data points and they are all weird).

That doesn’t mean it would have been a particularly good prediction at those past points, just that it was better than the alternative of just looking at the polls 20, 12 or 6 months out. The polls now are a snapshot of public support now, they are not a prediction of what will happen in May 2015. If polls move in the sort of way they have in the run up to past elections we can expect the Conservatives to significantly recover. If they don’t, then they won’t, simple as that. Polls do not move by magic, drawn towards past election results by some invisible force. If they narrow, it will be because of the economy, because of changing attitudes to the parties, because, perhaps, of different factors weighing upon people’s political choices as an election becomes more imminent… that, however, is a post for another day.

(*I should also add that this is NOT Steve’s personal prediction of the election – it’s an attempt to see to what degree you can predict election results months in advance using just national poll data. I expect if Steve was making a personal prediction he probably would ponder what the impact of the economy, the party situation etc would be, but that would be a very different and more subjective model.)