New ICM and YouGov polls
This month's ICM poll for the Guardian is out and has topline figures of CON 39%(+3), LAB 36%(-1), LDEM 15%(+1), Others 10%(-3). ICM normally show the best figures for the Liberal Democrats and the worst figures for Labour for methodological reasons, so it shouldn't be a surprise that they they putting Labour in a worse position than other recent polls, what is interesting is the direction of travel. While different polling companies have methodological differences that tend to favour one party or another, they normally all show the same direction of travel. YouGov's daily polls, ComRes, MORI and Angus Reid have all suggested a movement back to Labour in recent polls, this (and Opinium's last poll) show a movement back to the Conservatives. As such I'll add my normal caveat - sure, it could be the Tory boost... or it could be normal variation within the margin of error.
For methodology anoraks, it's also worth noting that this the first of ICM's monthly Guardian polls to include mobile phones in its sample. I don't know what, if any, impact that has on results (it may well, before anyone leaps to conclusions, be none whatsoever).
The other questions unsurprisingly looked towards this week's budget. On which team was best to run the economy respondents preferred Cameron & Osborne to Miliband & Balls by 42% to 25%. On prospective budget measures, 67% of people thought the 50p top rate of tax should be kept, 62% would support a mansion tax and 47% supported stopping child benefit for households with higher rate taxpayers.
UPDATE: YouGov's daily poll for the Sun meanwhile has topline figures of CON 36%, LAB 42%, LDEM 9%. Clearly no movement back to the Conservatives there.
Inevitably many of you reading this will be asking why the big difference. Well, there are a couple of obvious reasons. Firstly there is likelihood to vote. YouGov do not filter or weight by how likely people say they are to vote. ICM weight respondents by how likely they are to vote, and also weight down people who did not vote in the last general election. This helps the Tories and hurts Labour, and according to the Guardian's write up without the likelihood to vote weighting Labour would have been ahead in ICM's poll.
Secondly there is how the two companies treat don't knows. YouGov's figures are based only on how people say they would vote in an election tomorrow - people who say they don't know how they would vote are ignored. ICM on the other hand make an educated guess as to how the don't knows would vote, assuming that 50% of them will vote for the party they voted for in 2010. This normally gives the Liberal Democrats a significant boost.
Finally, there is normal margin of error, the random variation between one sample and the next that is unavoidable in all polls. Because we get daily polls from YouGov we can be fairly certain that their underlying average is a Labour lead of five points or so, and daily polls fluctuate randomly around that: today's is clearly a little bit more Laboury than of late. From ICM we have just the one monthly poll, but it's possible that normal variation has produced a sample slightly more Conservative than usual (it's equally possible that the sample is more Labour than usual, but that would hardly help explain the difference!).
Beyond this there are all sorts of other factors that produce variation between different polling companies figures (what figures they weight to and particularly what political weights they use, when the weighting data is collected, how they sample, what questions they ask, etc). All of these go together to produce the "house effects" of the different companies - which are more favourable to Labour or the Tories or the Lib Dems. Most of the time (with today being an unusual exception that I expect will vanish soon enough), all the companies show the same trend...and away from elections that's the thing to watch.
