ICM poll of Sheffield Hallam

ICM have released a new constituency poll of Sheffield Hallam, conducted for the Guardian. It shows Nick Clegg holding on to his seat by a margin of seven points over Labour when respondents are asked a voting intention question that includes the names of the candidates standing. Full details are here. As regular readers will recall, previous polling of the seat has shown a much tighter race with Lord Ashcroft's last poll in Hallam showing Labour ahead by one.

So which poll is correct? Is Nick Clegg likely to hold his seat? The bottom line is while that this piece of evidence does make it look a little more likely that Clegg might hold on, we can't really be confident what the true position is. The ICM poll had a sample size of 500, the Ashcroft poll had a sample size of 1000. Hence it could well be that there isn't any difference at all between the polls, that it's just normal sample variation around a small Lib Dem lead. Its also possible that there has been movement towards Clegg in the days between the two polls as the election looms and people consider a tactical vote.

However a lot has been made of the fact that while both polls had an effort to take account of people's personal and tactical voting behaviour in their own constituency, they did so in different ways - Ashcroft asks a two stage question, asking people their national preference and then how they will vote thinking about the candidates and parties in their own constituency; ICM asked people the voting intention question including the names of the candidates standing in Sheffield Hallam. Both methods seem to have given a boost to the Lib Dems compared to a generic question, given sample variation and timing we can't even be certain one did had more impact than the other, let alone which one is more accurate.

One can very easily make a case for one or the other method (Chris Hanretty has a good go here) but really that's only theorising, we can't know which way is better unless you test it against some actual elections, and at previous elections constituency polling has been a rare commodity.

In the meantime, Sheffield Hallam remains an interesting race. Normally the idea of party leaders losing seats is regularly drummed up but incredibly unlikely to happen. This time, while my personal expectation is that Clegg will hold on and this poll will probably end up about right, there is a least a non-zero possibility of him being ousted. We shall see.