ComRes poll of alternate Labour leaders
The part of tomorrow's ComRes poll that will no doubt get the most attention is a series of questions asking how people would vote with a different leader. These appear to show that Labour would do better with any alternate leader, and that most of them would produce a hung Parliament instead of a Conservative victory. Looking more carefully though, the figures don't appear to be comparable, and shouldn't be compared to standard voting intentions or taken as voting predictions.
Generally speaking the "how would you vote if X was leader" sort of question is very popular with the press, but there are a bucketload of problems in carrying them out and interpreting them. Firstly, there is how to ask them. A normal voting intention question does not mention the leaders of the party by name, and adding their names does have an effect (Populus tested it when it was all the rage to ask questions about how people would vote with Brown as leader). Therefore one cannot ask "how would you vote if X was Labour leader" and then compare it to the standard voting intention question, since that did not include Gordon Brown's name in the question, and would have given a different answer if it had.
On top of that, just including the name of the putative Labour party leader in the question itself skews the question, because it is not mentioning the names of David Cameron or Nick Clegg. Mention one, you should mention them all (and that too makes a difference, so shouldn't be taken to seriously either.)
Thirdly, there is whether the questions are asked on an equal footing. For most of the polling companies voting intention is actually quite a cumbersome question, they ask how likely people are to vote, how they would vote, and in some cases a squeeze question too. If you want to ask a series of truly comparable "alternative leader" questions you'd need to ask again how likely people are to vote with each leader, then who they would vote for. Understandably this is sometimes skipped and it assumed that likelihood to vote remains the same, but that's probably a false assumption.
Even if you do all this, it's questionable how meaningful the answers are. People probably have a fair idea of what Jack Straw or Harriet Harman are like, they've both been in the public eye a long time... but Ed Miliband? Equally, while they may have an idea what sort of chap Jack Straw is, few have any real idea of what he, or any other alternative leader, might actually do were to to become Prime Minister or, to be honest, how they would react to it.
So, with all that in mind, let's turn to the actual questions in the ComRes poll. ComRes asked "If there were a general election tomorrow, which party would you vote for if each of the following were leader of the Labour Party?", so the question prompted by the name of the Labour party leader, but not the leaders of the other two parties. Most importantly their standard question is filtered and weighted by turnout, however as far as I can tell the questions for alternative leaders weren't.
In other words, the questions aren't comparable. Filtering by likelihood to vote almost always helps the Conservatives and hurts Labour, so it's no great surprise that questions that aren't filtered by likelihood to vote show Labour doing better (and that's before the effect of prompting by only the Labour leader's name is taken into account). We cannot conclude from these questions that the alternative leaders would do better than Brown.
What the poll is useful for is comparing the alternate Labour party leaders to one another. It's not that useful of course, since several of the people asked about aren't very well known to the public and the public are not necessarily very good at predicting what they would do or how they would perform if they did become Prime Minister. For the record though, Jack Straw did the best, followed by David Miliband, closely followed by his brother Ed. Behind that was Ed Balls and Harriet Harman, then Alan Johnson, then Peter Mandleson. The least impressive figures were for Jon Cruddas, probably because he is the least well known.
