Curious casting: how accurate are the polls?
Updated on 30 April 2010
It is interesting looking at some of the instant post-debate reaction polls, writes Political Editor Gary Gibbon. Some are weighted to match what the pollsters think is the profile of people who watch the debates.
YouGov have been very open, saying that it means they tend to include more prosperous voters, more broadsheet readers, older voters, who are slightly more Conservative and sometimes more male-dominated than the voting population as a whole.
ComRes doesn't weight to viewers but to the voting population profile.
Look at how the ComRes poll sample for last night worked. They polled people who expressed their voting preference as 35 per cent Conservative, 24 per cent Labour and 36 per cent Liberal Democrat.
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.
More election news from Channel 4
- Leaders' debate: the final curtain call
- More from Gary Gibbon on the leaders' debate
- Tony Blair joins the Labour campaign trail
- Poll of polls: Still all to play for
- Leaders' debate: the verdicts on who won
As Michael Howard's posters used to say in 2005, "Are you thinking what I'm thinking?".
ComRes point out that if you look at their sample for previous debates the numbers do jump about more.
People with stated allegiances sometimes cross over and say they think a rival leader did better. But you see the point.
These polls are hugely influential. The debates are now a big part of our national political life.
But we need to know what we are looking at when we read them and, a question for further down the line, we need to make sure the debates don't become our entire national political life in future campaigns.
Should they be run by independent bodies as in the US? Should there be more opportunities for challenge?
Compare what happened when the politicians nervously dipped their toes in this whole business with the "Ask the Chancellors" debate on Channel 4. They insisted on strict rules - and Vince Cable won.
Look at the later BBC "Daily Politics" debate, with Andrew Neil and Stephanie Flanders conducting a much more interventionist, more conventional British TV debate - and Vince Cable lost.
This is not making a point about any of the organisations or individuals concerned.
But you can see how both the rules and the dynamics of the party leaders on the stage - how they want to play it, who they want to attack or cuddle up to - can dictate the level of scrutiny or challenge.
There's a lot more to say on this, and a big debate will start after the election - about how the debates combined with the convulsion of the polls, and the spectre of a hung parliament, meant we got less policy in the coverage and more polls and process.