Earlier in the week we also saw the publication of this article by Martin Boon and John Curtice, their take on why the polls overestimated the Lib Dems at the last election, based upon a call back survey of 1,200 of the respondents to their final survey.

The first reason Boon & Curtice suggest is a late swing, though they see this as explaining only part of the error. 95% of people who told ICM before the election they were going to vote Conservative reported actually having done so after the election, for Labour the figure was 93%, for the Lib Dems it was somewhat lower at 87%. That said, they say that the number of people switching towards the Lib Dems was almost as much as they lost, so this can only be a small factor.

Secondly, Boon & Curtice do not think differential turnout was a big factor. People who said they were going to vote Lib Dem before the election were not significantly more likely to tell ICM in the post election poll that they didn’t vote.

Thirdly, ICM’s don’t knows disproportionately brokein favour of Labour, backing ICM’s decision to use their “spiral of silence adjustment” (Boon & Curtice still refer to this as “shy tory syndrome” in their article, though in this case it was “shy” Labour voters). One of the conclusions they draw in the article is that it may be better to make the adjustment even stronger.

Finally, Boon & Curtice say ICM may have weighted the Lib Dems too highly in their past vote weighting, and that this will be high on the list of their investigations in coming months.

It is also worth reading Roger Mortimore of Ipsos MORI’s reply in the comments to the article, where he makes a very valid point that underlines just how difficult it is to work out for certain what went wrong with the polls – many factors that could have skewed the final polls could also have skewed any call back survey. To take Roger’s example, if the problem was people saying they would vote Lib Dem but not actually doing so on the day, those people might also have claimed to have voted when they didn’t in a call back survey.

In that specific case, we will eventually have concrete evidence of whether differential turnout was a problem or not (the British Election Study recontact interviewees after the election and ask if they voted, but also check them on the marked electoral register to see if they really voted), but there are similar problems we will never be able to rule in or out for sure. If, for example, some people told pollsters they would support the Lib Dems but actually voted for someone else (for whatever reason – being the fashionable thing to say perhaps), they may have said Lib Dem in the ringback survey for that same reason.

UPDATE: And on more topical matters – tonight’s YouGov voting intentions are CON 42%, LAB 34%, LDEM 17%.

I have now updated the swingometers on the site with 2010 election data.

Dull old text version here – http://ukpollingreport.co.uk/blog/swing-calculator
Lovely graphical version (but needs a plug-in for Internet Explorer) – http://ukpollingreport.co.uk/blog/swingometer-map
Enhanced graphical version with seperate swings for Scotland and Wales – http://ukpollingreport.co.uk/blog/advanced-swingometer-map

Of course, these may turn out to be of purely academic interest, since the government still seem to be intending to reduce the number of seats by 10% in time for the next election, and that’s leaving aside the possiblity that the voting system itself is changed. We shall cross those bridges when we reach them though!

Seats where the Conservative share fell
There were 75 seats where the Conservative share of the vote fell. Their biggest falls were Westmorland and Lonsdale (the effect of Tim Farron building up a mountainous personal vote), Bromsgrove (presumably the result of Julie Kirkbride’s expenses – though there were two other cases of ethnic minority Conservative candidates inheriting safe seats and receiving a lower share of vote), Sheffield Hallam (the Clegg factor no doubt), Folkestone and Hythe (probably the loss of Michael Howard’s personal vote as leader), Castle Point (where the former Conservative MP Bob Spink split their vote).

Biggest Conservative increases
The biggest Conservative increase was 16% in Hartlepool, taking second place from the Liberal Democrats (probably the by-election factor slowly unwinding), followed by Montgomeryshire (where Lembit Opik fell), Esher and Walton, Crewe and Nantwich (the by-election effect), Cardiff Central (a strange one there, the Conservatives are in third place), Camborne and Redruth (unseating Julia Goldsworthy from third place).

Seats where the Labour vote rose
There were 80 seats where Labour increased their share of the vote – over half of these were in Scotland, many others were seats with a large Muslim population where the Iraq war effect in 2005 seemed to reverse somewhat. The biggest increases in Labour’s vote were Blaenau Gwent, where they reclaimed the seat from the Independent MP, East Ham and West Ham (where Respect performed well in 2005 but did not stand in 2010), Glenrothes (after the successful by-election defence), Dunbartonshire West, Edinburgh West (where they took second place from the Conservatives) and Bethnal Green and Bow (another of the three Labour Gains).

Biggest Labour falls
The biggest drop in the Labour vote was 24% in Barnsley East, a seat so safe they probably barely felt it. The main beneficiary there was a new BNP candidate. This was followed by Hemel Hempstead (putting them into 3rd place in a seat they held till 2005), Redcar, Don Valley (making Caroline Flint’s seat a marginal – the votes went to new BNP, UKIP and English Democrat candidates), Norfolk North West (where their candidate went spectacularly off message in the days before the election), Cannock Chase (the “safest” Labour seat that was won by the Conservatives) and Normanton, Pontefract and Castleford (Yvette Cooper’s seat).

Biggest Lib Dem increases
Three seats stand out with huge increases in their vote – most notably the incredible performance in Redcar, Mo Mowlam’s old seat, which fell on a 21.8% swing, wiping out a 31% majority – presumably on the back of the mothballing of the Corus steelworks. Almost as large was the increase in the Lib Dem vote in Ashfield, Geoff Hoon’s old seat inherited by Gloria de Piero, which the Lib Dems only narrowly missed out on. Less remarked upon was a 17% increase in the Lib Dem vote in Merthyr Tydfil and Rhymney. After that the best performances were Dunfermline and Fife (by-election factor, though not enough to hold the seat), Westmoreland and Lonsdale (the Tim Farron effect), Ceredigion, Maidstone and the Weald, Brent Central (Sarah Teather gambling on going for the difficult option when her seat was abolished… and making the right choice).

Worst Lib Dem peformances
The biggest drop was Orpington, where they lost whatever following their candidate Chris Maines had built up after fighting the seat hard at multiple elections. Following that their worst performances were Edinburgh West, Hartlepool (fading by-election effect), Montgomeryshire (Lembit Opik) and Haltemprice and Howden.

Biggest swings from Lab => Conservative
36 seats had a swing from Labour to Conservative of over 10%. The biggest were Hemel Hempstead (CON HOLD – 14.4%), Cannock Chase (CON GAIN – 14%), Barnsley East (LAB HOLD – 13.9%), Crewe and Nantwich (CON “GAIN” – 13.7%), Norwich North (CON “GAIN” – 12.9%), Hartlepool (LAB HOLD – 12.8%), Sittingbourne and Sheppey (CON “HOLD” – 12.7%). The biggest swings in the other direction were Blaenau Gwent (-7.7) and East Ham (-7.7).

Biggest swings from Lab => LD
There were 29 seats with a swing from Labour to Lib Dem. The biggest were Redcar (LD GAIN – 21.8), Ashfield (LAB HOLD – 17.2), Merthyr Tydfil (LAB HOLD – 16.9), Barnsley East (LAB HOLD – 14), St Albans (CON HOLD – 13.8), Bosworth (CON HOLD – 13.8), Norfolk North West (CON HOLD – 13.3). Note some of those movements beneath the surface where the Conservative MPs vote remained pretty unchanged but the Lib Dems overtook Labour and took a strong second place on large Lab=>LD swings. The biggest swings in the other direction were mostly in Scotland, the largest were Edinburgh West (-11.3), Orpington (-9.5) and Paisley and Renfrewshire North (-8).

Biggest swings between Con and LD
The largest swings from LD to Con were Hartlepool, Montgomeryshire, Orpington, St Ives and Cardiff Central. The biggest swings in the other direction were Redcar, Westmoreland and Lonsdale, Ashfield and Dunfermline and Fife.

Highest shares and lost deposits
The Conservatives won 125 seats with over 50% of the vote. The highest were Richmond Yorkshire (62.8%), Beaconsfield (61.1%) and Windsor (60.9%). They lost their deposit in two seats, Glasgow East (4.5%) and Na h-Eileanan an Iar (4.4%).
Labour won 76 seats with over 50% of the vote. The highest were Liverpool Walton (72%), Knowsley (70.9%), East Ham (70.4%). They lost their deposit in 5 seats, all tight LD-v-Con marginals: Eastbourne (4.8%), Somerton and Frome (4.4%), Newbury (4.3%), Cornwall North (4.2%), Westmorland and Lonsdale (2.3%).
The Liberal Democrats won 12 seats with over 50% of the vote. The highest were Orkney and Shetland (62%), Westmorland and Lonsdale (60%), Bath (56.7%). They managed to save all their deposits, with their lowest share of the vote being Glasgow East (5%).

Minor parties and Independents
The BNP saved 72 deposits. Their strongest performances were Barking, Dagenham and Rotherham. UKIP saved 98 deposits, their strongest performances were Buckingham, Boston and Skegness and Christchurch. The Green party saved 7 deposits – their best performance was obviously Brighton Pavilion, followed by Norwich South.
The English Democrats put up 107 candidates and saved 1 deposit in Doncaster North (5.2%). The Christian party put up 70 candidates, and lost all their deposits. Their highest vote was 1.8% in Inverness, Nairn, Badenoch and Strathspey.
The highest votes for Independents and others were obviously Buckingham, Wyre Forest, Castle Point (where Bob Spink did surprisingly well for a former MP standing as an Independent) and Blaenau Gwent. Less obvious strong performances came in Makerfield, Mansfield, Hemsworth, West Ham, Dewsbury and Sleaford and North Hykeham.

Safest seats, closest marginals
The safest seats are Liverpool Walton (Lab, 57.7%), Knowsley (Lab, 57.5%), Liverpool West Derby (Lab, 56.2%). The safest Lib Dem seat in Orkney and Shetland (51.3%). The safest Conservative seat is Richmond Yorkshire (43.7%). There are 40 seats with majorities under 1000, including 5 with majorities under 100 – Thurrock (92), Bolton West (92), Camborne and Redruth (66), Warwickshire North (54), Hampstead and Kilburn (42). All the figures on this post are based only on Great Britain – in Northern Ireland we had the narrowest majority of all, 4 votes in Fermanagh and South Tyrone.