Interesting post from Gary Gibbon, political editor at Channel 4 News, as he sheds some light on those post-debate polls. Not the daily, party-based opinion polls but those conducted by many of the same firms immediately after the weekly debates finish.
Take one from last night:
[ComRes] polled people who expressed their voting preference as 35 per cent Con, 24 per cent Lab and 36 per cent Lib Dem. And here's how those same people voted on the instant poll on who performed best in the debate: 35 per cent Cameron, 26 per cent Brown and 33 per cent Clegg. As Michael Howard's posters used to say in 2005, "Are you thinking what I'm thinking?"
Isn't there more than a possibility that voters are simply voting for their man, regardless of performance?
A quick call to ComRes helps clarify how it conducts these surveys.
First it identifies a sample of 2,000 people broadly reflecting the demographic of the electorate, albeit only those intending to watch 90 minutes of hardcore politics. All 2,000 receive an automated call within five minutes of the debate finishing, and each is asked two standard questions -- who do you think won the debate? how are you intending to vote? -- plus two topical questions. (Yesterday there was one about public services and one, inevitably, about Bigotgate.)
ComRes says that in the first two debates there was a much wider discrepancy between the voting intentions of its sample and who they thought had won the debate. And there's little doubt that those post-debate surveys two weeks ago detected the first stirrings of Cleggmania.
The company does accept, however, that as election day gets nearer, and people's voting intentions solidify their debate verdict could well be dictated by personal preference.
ComRes is not the only firm under the spotlight. As Gibbon notes:
YouGov have been very open, saying that means they tend to include more prosperous voters, more broadsheet readers, older voters, to be slightly more Conservative and sometimes more male-dominated than the voting population as a whole.
Given how influential these polls are in setting the agenda -- witness this morning's near-uniform newspaper headlines and the way the debate was treated on the Today programme - it seems that all polling organisations will need to review how they conduct these surveys.
It's not just the politicians and the broadcasters that are feeling their way.