By David Cowling
Editor, BBC political research unit
Ronald Reagan was the only clear beneficiary of the US debates
Will the televised debates between the three main party leaders have any impact on the outcome of the general election?
If the experience of the US presidential candidates debates is anything to go by, our answer would have to be "not much".
Gary Langer, head of polling at ABC News, has analysed public reaction as expressed in opinion polls sampled after the debates and investigated whether they changed anything.
On the most measurable indicator - increased support for candidates - there appears to be only one debate that made a real difference.
That was in 1980 when Ronald Reagan overturned an eight-point campaign lead for President Carter, jumping three points ahead in a post-debate poll.
However, Gary makes the point that there can be more subtle outcomes to the debates than simple changes in top-line voting figures.
"They are, after all, an essential window on the candidates' styles and grasp of issues alike,"
he says in his blog.
He cites various examples of this including, in the most recent debates of September/October 2008, polls suggesting that Mr Obama improved his ratings as a "safe" choice for president as a result of his performances.
Mr McCain, on the other hand, seemed to suffer from an increase in the numbers who thought he would be a "risky" choice.
PRIME MINISTERIAL DEBATES
Domestic affairs: ITV - 2030GMT, 15 April
International affairs: Sky News - 2000GMT, 22 April
Economic affairs: BBC One - 2030GMT, 29 April
But what is the public mood prior to our own prime ministerial debates?
So far, the polls suggest that a lot of people intend to watch at least one of them: 57% according to ICM/News of the World (sampled 3-4 March) and 54% according to Populus/Times (sampled 12-13 April).
If that translated into actual voters, that means the debates would reach far more than 20 million people. We shall see.
In the battle of expectations, David Cameron is already the victor.
Populus/Times found 42% expecting him to win the debate, compared with 22% who thought Gordon Brown would be the winner.
However, as a consequence of this, Mr Cameron faces a real problem: It is all for him to lose.
He may perform very well but that is what everyone expects and so he may not gain any great bonus from his performance.
On the other hand, such are the low expectations of Mr Brown that he need only deliver a decent performance to come across as a relative Emmy award nominee.
Nick Clegg needs to perform well, not only to differentiate himself from the other two leaders but also to prop up the 23% of the national vote his party received at the last election.
However, some critics believe his recent performances in big set-piece debates in the Commons have been weak and that these televised debates may not be the best forum for his talents.
As the polls have narrowed in the run-up to this campaign, more and more people seem to view these debates as key to the outcome.
I confess to being a sceptic on this.
Britain's political system is profoundly based on a Parliament, not a presidency.
Doubtless every word, every gesture, every twitch of a facial muscle will be pored over and analysed following each of the three debates.
Sound bites will be extracted and broadcast in a perpetual cycle. A series of distinguished commentators will be interrogated about what it all means.
But whether any voter will emerge from the debates better informed about the detail of what each of the three main parties has in store for us if they win, I beg leave to doubt.
I hope I am wrong.
I hope the debates prove interesting, informative and entertaining and motivate many millions of people to vote on 6 May.
It's just that I won't be betting our mortgage on such an outcome.