MORI’s political monitor for May is out. The topline figures with changes from last month are CON 37%(-1), LAB 35%(+4), LDEM 18%(-2). The fieldwork for the poll was actually conducted prior to the recent YouGov and Communicate Research polls, but the trend matches that of the other polls since Tony Blair’s announcement of his retirement – a boost for Labour, slightly more at the expense of the Liberal Democrats than the Tories.

UPDATE: A late entrant for the “Atrocious press coverage of opinion polls” award! The Daily Express reports the poll as showing the Tories slumping from “42% to 37% since last month” (that’ll be down one point from 38% last month) “after a fortnight of Conservative feuding over grammar schools” (that’ll be in a poll entirely conducted within a week of David Willett’s original speech).

Communicate’s May poll for the Independent has topline figures with changes from last month of CON 35%(-1), LAB 31%(+4), LDEM 19%(-3). This largely reflects the trend seen in the other May polls, which have seen a Labour recovery, most often at the expense of the Liberal Democrats – although it is worth adding that in this case of Communicate Labour are recovering from an exceptionally low figure last month.

UPDATE: Several more things – firstly I still haven’t seen the details of how Communicate weight their polls by past vote, but looking at their tables they seem to weight people who voted for “other” parties in 2005 very highly. In reality 8% of people in Great Britain voted for a party other than the main three. Because of false recall ICM and Populus weight their samples so that amongst voters the share is actually lower than that at around 7%. Amongst those who voted in Communicate’s sample 12% of people reporting voting for an “other” party in 2005. Perhaps this explains the rather low shares of the vote for the main parties.

Secondly, Labour voters seem to be much firmer than usual in their intention to vote. The normal pattern is that Conservative and Lib Dem voters say they are more likely to vote than Labour voters do. In this poll the Tories, as usual, had the most committed voters, with 64% of Tory voters saying they were 10/10 certain to vote, but Labour were very close behind with 60% of their voters 10/10 certain. To some extent the increase in Labour support since Blair’s resignation does seem to be down to a re-invigoration of existing Labour supporters. It is the same if you look at the detailed tables of ICM’s last two polls, on ICM’s figures without turnout weighting they would have been up just one point, with turnout weighting they go up two.

Finally a lot of newspaper coverage has taken up the question on whether Brown or Cameron would be more likely to keep their party united, where Brown led by 40% to Cameron’s 37%. This is being widely contrasting to a question from a Communicate poll at the end of last month where 64% of respondents said they thought Labour were divided and 36% thought the Tories were.

For a whole barrel load of reasons it isn’t comparable in the slightest. The question last month asked people to say which parties were divided, they could have picked all three if they wanted. Today’s question asked people to pick either Brown or Cameron, you couldn’t pick both. The question last month asked about the parties as they are now, the questions published today ask people what they think will happen in the future. The questions last month asked about the parties and how united they were, the questions published today asked about the abilities of Brown and Cameron to deal with and contain such division.

In the defence of the media, I haven’t spotted anyone drawing a direct comparison between the two questions, but I’m certain that is meaning many people who hadn’t read either of the questions would take away. If you want to draw a trend from one month to the next, the questions have to be comparable.

More from this month’s YouGov poll in Monday’s Telegraph , largely about public perceptions of Gordon Brown. The overall findings contain nothing new – Brown is seen as intelligent, effective, competent and decisive, but also divisive, gloomy and dull.

More interesting is whether or not the leadership campaign (if you can call it a campaign without any rivals) so far has succeeded in improving Brown’s image. 22% of people said that Brown had made a favourable impression upon them since announcing his candidacy, 20% said he had made a negative impression – I suspect those answers will be largely partisan, with the 22% of positive answers mostly existing Labour supporters backing “their guy”. More interesting is the way the answers to the questions about Brown’s public image have changed since they were last asked in September 2006.

First the positives: Brown’s net scores on being effective and competent have barely changed since last September at +10 and +28 (compared to +11 and +27 in September), his net score on being decisive is up to +35 from +28 in September. Some of Brown’s negatives are also unchanged – he isn’t any more trusted than in September (-18 now, -19 then), and is barely seen as more able to unite the country (-31 now, -33 then) or cheerful (-32 now, -34 then).

In some areas those his public perception has improved. His net score on being “concerned for the country as a whole” rather than just himself was minus 23 in September 2006, now it is only minus 10. His net score on being caring was minus 6 last September, now it scrapes into positive territory at plus 1. Finally, the big question of whether Brown has made himself any more likeable – back in September his net score was minus 19, now it is only minus 8.

So, has the Brown PR offensive made people warm to him? Certainly they seem to like him more than last September, but I’m not quite sure it’s down to the last couple of week’s activities. The September questions were conducted just after Tom Watson’s resignation, widely percieved as an abortive “Brownite coup”, with saw perceptions of Gordon Brown drop sharply. The increase in Brown’s ratings since then could just as much be the result of his image recovering from the events of last September and they could be the result of the last couple of weeks’ campaign. Still – I can’t image all these same sort of questions won’t be asked again when Gordon Brown becomes Prime Minister and we’ll see then if his image really has improved.

Despite the major differences between the methodology used by the different pollsters, by hook or by crook the voting intention figures they produce all tend to be relatively similar to one another. The exception is the Liberal Democrats, who vary significantly between ICM, who give them the highest scores, and YouGov, who give them the lowest. In a post earlier this year I calculated the average difference between the Lib Dem scores from the two pollsters to be 3.0%. Perhaps this is made even more noticable because it does make it difficult to judge how well the Lib Dems are doing – there are sometimes significant differences between the pollsters Labour or Conservative scores, but since recently the overall picture is always one of a Conservative lead over Labour it doesn’t really change anything. When it comes to the Lib Dems all the polls show thenm down on the last election, but with ICM is a relatively small fall, with YouGov they appear to have been mercilessly squeezed.

Several people have asked what the reason might be – including a post my Mark Park on Libdemvoice here – and which figure (if any) is right? Unfortunately these are no easy answers to who is right, but I can at least flag up some potential reasons:

Mode of questioning. ICM and Populus ask people over the phone, YouGov ask people online. In lots of cases people might give an answer to an anonymous computer screen that they would be embarrassed to give to a live interviewer on the other end of a phone line. Obvious cases are extremist parties like the BNP, but small fringe parties suffer in general because people are unsure about going out on a limb. With a mainstream party like the Lib Dems this shouldn’t be a factor…but actually it could be having a knock-on effect. Some support for the Liberal Democrats isn’t positive support for their ideas or policies, but a “neither of the above” vote. Potentially some of the higher support for the Lib Dems in phone polls could be “neither of above” voters who might really be tending towards fringe or extreme parties but are unsure about naming a fringe party to an interviewer. Given that YouGov tend to have a higher “other” score than other pollsters though, this might well be a factor.

Don’t knows. ICM and Populus both do an adjustment to their figures to take account of don’t knows. Based on past studies they assume that a proportion of don’t knows will actually end up voting for the party they did last time round. People normally think of this as an adjustment for “shy Tories”, but the net effect these days is rarely if ever to help the Conservatives. For the last couple of years it has normally helped Labour. The way it works though will help any party who finds that some of their past supporters have drifted away and are now telling pollsters they don’t know how they’ll vote. In ICM polls 50% of previous Lib Dem voters who now say “don’t know” are added onto the Lib Dem score, in Populus polls they re-allocate 30% of previous Lib Dem voters. Does this increase the level of Lib Dem support in ICM polls? Because ICM publish the figures before and after the adjustment this is one area where we can quantify the difference – some observers have taken the difference as having emerged after December 2005, so taking the 18 monthly ICM polls since then, the adjustment has been large enough to increase the Lib Dem score by 1 point six times, and has reduced it by 1 once – so on average it increases Lib Dem support by 0.28 of a percentage point, leaving another 2.72% difference to be explained by other factors.

Likelihood to vote. Uniquely amongst the pollsters YouGov do not filter or weight by likelihood to vote. If Lib Dem supporters were actually more likely to vote than supporters of other parties then this could explain some of the difference. In fact, it’s normally Tory supporters who are most likely to vote, followed by the Lib Dems with Labour supporters further behind – so perhaps this could be contributing to a lower level of Lib Dem support in YouGov polls? Again, by looking at the figures before weighting by turnout in ICM’s detailled tables we can quantify this – since December 2005 ICM have published the breakdown for likelihood to vote from 11 of their Guardian polls. If you compare what the rounded figure would have been without turnout weighting, and what it actually was afterwards, 2 times it increased the LD score by a point, 2 times it reduced it…so it has no overall effect at all. Even with MORI’s very harsh filter by turnout it makes only a minimal difference.

Sampling. Could there be a difference from the sampling techniques? Could the people who pop up in a telephone poll be more likely to be Lib Dem voters than people who join an online polling panel? In terms of political activists it probably works the other way if anything, but when it comes to normal voters who knows? It is possible, but given than both ICM and YouGov weight their polls politically it this was a problem it would be something that the pollsters should be able to address using political weighting – if YouGov’s sampling produced too few Lib Dems they would weight they upwards, if ICM’s produced too many they would weight them down (though in actual fact ICM tends to weight the proportion of part Lib Dem voters upwards, sometimes quite heavily). That bring us to…

Weighting targets. This is potentially where most of the difference lies. I suspect that when pollsters weight their polls politically ICM and Populus are weighting their sample to have a slightly higher proportion of past Lib Dem voters than YouGov are. Unfortunately it is impossible to directly compare the proportions used because ICM and Populus weight using recalled past vote and YouGov weight using party identification.

The data used for political weighting. This is the most subtle difference, and the one that I suspect is behind a fair amount of the difference. Phone polls do their political weighting based on data that is collected now. They then have to take account of false recall and forgetfulness when drawing up weighting targets. In contrast YouGov weight their polls using the data they collected back in May 2005 when it was fresh in respondents minds who they had actually voted for that day. The people who voted Lib Dem in 2005 but who don’t recall or say they voted for a different party if you ask them now are, perhaps not surprisingly, also far less likely to say they would vote Lib Dem in a general election tomorrow. In other words, the past Lib Dem voters that phone pollsters find are the more committed Liberal Democrats. “Flakier” Liberal Democrats who are more likely to switch to other parties are more likely to have forgotten they voted Lib Dem in the first place. Those identified as Lib Dems in YouGov’s samples probably contain more of those “flaky” Lib Dems than those identified as Lib Dems in phone samples.

What is the ultimate reason for the difference? I don’t know. It looks as though we can rule out likelihood to vote weighting and we can see that the “spiral of silence adjustment” is only a very small factor. The mode of questioning may be having some effect – people who say “Liberal Democrat” to a live interviewer might be willing to admit to a computer screen that they will actually vote for a smaller fringe party. In my opinion the difference is more likely to be somewhere in the weighting, and here is it almost impossible to draw any conclusions – ICM and YouGov weight using a different measure, based on data collected at different times and, as with all political weighting, chosing the targets they weight to is as much an art as a science.

Who’s right? It is impossible to say. If the reason had turned out to be something to do with likelihood to vote then you could have a rationial discussion about to what extent and how turnout should be factored in, ditto the way don’t knows are dealt with. It really is very difficult to make informed judgements about weighting. I am not one who believes that is any accurate way of telling how well parties are doing apart from polls: people vote differently in general elections to local elections; even if they were a decent guide, we must be approaching a record period without a Parliamentary by-election; local by-elections don’t even seem to be a good guide to local elections these days, let alone anything else! The only reliable way to tell which poll is producing more accurate results will be to wait until the next general election and see what the actual results are. Sadly, they doesn’t help you much in deciding who is right now.

I’ll give you two warnings. Firstly, it isn’t always the poll that is different from the rest that is wrong. In 1992 Harris was showing a Tory lead when everyone else had Labour ahead. People dismissed Harris as being wrong, the rest is history. Secondly, it is very tempting to believe the poll you want to believe – to see fault in every detail of the methodology of the poll who you really hope isn’t right and the obvious superiority of the poll you hope is true. In few if any cases do I think that people are deliberately talking up polls that favour their own party. I just think that somewhere deep in our subconscious we all tend to will ourselves into finding arguments in favour of the methodology that produces the results we like more convincing :)

YouGov May Poll

In the strange interregnum between Blair’s resignation announcement and Gordon Brown’s accession it’s still unclear what the polls signify. In the three polls carried out since Blair stepped down Labour have received a boost in the polls – either at the expense of the Liberal Democrats or the Conservatives. It is impossible to say for sure precisely what is behind most changes in the opinion polls, but personally I suspect this shift was a “Blair boost” – a result of more positive opinions otwards Tony Blair now he is going (there were similar spikes in his scores when he first announced he wouldn’t be seeking a fourth term and after his final conference speech as leader last year).

Today’s YouGov poll for the Telegraph has the Conservative lead back up to 6 points again with topline figures (with changes from YouGov’s last poll – conducted for the Sunday Times just after Blair’s announcement) of CON 39%(+1), LAB 33%(-1), LDEM 15% (nc). The individual changes in voting intentions are not significant, but there doesn’t appear to be a continuing movement towards Labour, if anything things are drifting back to the Conservatives.

I was asked a week or so ago about what I thought would happen in the polls during this period. I said I expected a Blair boost (we one we’ve already seen) followed by a Brown boost from the positive publicity accompanying his rather strange lone leadership campaign and his eventual accession. Perhaps there would be a delay between them and Labour would go up-down-and-up-again, or perhaps they would blend together into one big jump. This pause in Labour’s advance therefore doesn’t necessarily mean that this is their boost from the leadership change and it’s all over – I suspect they’ve got more to come as opinions of Brown improve (temporarily at least). That said, the pause in Labour’s advance could be because the Conservatives have managed to reclaim the media agenda recently with their arguments over selective education – over at Political Betting Mike Smithson think that having David Cameron in the media whether it’s a good or bad story helps the Tories.

Another possible explanation is the different methodology between the pollsters – YouGov’s poll do not include any adjustments for likelihood to vote, ICM, Populus and MORI do. If Labour’s increase in the polls is largely due to Labour supporters being more enthused and saying they are more likely to vote, it wouldn’t make any difference to YouGov’s topline figures. Or – of course, it could just be the normal random variation between polls and not mean much at all!

Meanwhile there are already signs of improvement in perceptions of Brown. On the “Best Prime Minister” question Gordon Brown has caught up and overtaken David Cameron, who he now leads 30% to 27% (with 6% opting for Menzies Campbell). He has also narroed the large Conservative lead on the “forced choice” question of whether – if pushed – people would choose a Conservative government under Cameron or a Labour government under Brown. Cameron’s Tories now lead by only 3 points from a 10 point lead last month. With media focus on the man who has been Chancellor of the Exchequer for ten years, Labour have also moved back ahead as the party most trusted on the economy.