One of the oddities of the Scottish "leaders'" debate tonight was that it started with the results of an opinion poll. As it happened, that worked very much in Angus Robertson's favour, as it showed the SNP clearly ahead of both the Lib Dems and the Tories, thus portraying the party as the main alternative to Labour. But as a matter of principle I think it was the wrong thing for STV to do. It plants ideas in the minds of the viewers right from the outset about which parties are well-regarded and which aren't, and that must inevitably skew perceptions of the debate that follows. The whole purpose of a debate should be to allow the public to take a 'clean slate' look at the merits of each party and make their own minds up.
Which raises a broader question with particular relevance tonight - how much does the reporting of opinion polls during an election campaign not merely inform us about the state of public opinion, but actually influence the state of public opinion by creating a sense of momentum? Tonight, there are four new GB-wide polls, three of which show a continuation of the pattern of recent days, with a very tight battle for the lead between the Tories and the buoyant Liberal Democrats. Unfortunately, it's the fourth poll - which looks very much like an outlier - that is in danger of receiving all the attention simply because it was commissioned by a TV news programme. That poll shows the Tories opening up a nine-point gap on both the Lib Dems and Labour. Will the disproportionate coverage for this one poll generate an artificial sense of momentum for Cameron, and thus alter public opinion in the coming days?
Perhaps the French have the right idea - simply ban polls during the campaign, and let the public focus on the issues and not the horse-race. Yes, poll figures would still leak out on the internet, and anyone who really wanted to know what was going on could keep themselves very well informed, but there wouldn't be anything like the same distorting impact on the campaign.
It's not an issue I have a fixed view on, but it's certainly worthy of thought.