Leaders debate polling

Tonight is the seven-way leaders debate - we had the Paxman interviews a week ago and the opposition leaders debate and leaders question time to go, but tonight is the closest thing to the big set piece debates of 2010 that we are going to get in the 2015 election (at least it is in Great Britain as a whole, next week has the Scottish leaders debate in, well, Scotland).

Following the debate we should be getting four instant reaction polls proclaiming a "winner", from YouGov, ComRes, Survation and ICM. There will also be an Ipsos MORI worm, but they aren't doing a verdict poll.

In terms of reading what they mean, the default position tends to be party supporters thinking their own leader wins - if we get a result that largely shows Tories think Cameron won, Labour voters think Miliband won, Ukippers think Farage won and so on, then it's probably not going to change much. In the 2010 debate that sparked "Cleggmania" Clegg was winning by about twenty points in post-debate polls.

Secondly, remember winning the debate isn't necessarily a good guide to any impact in voting intention. The 2010 debates produced a big short term effect on the polls, even if it deflated by the election itself. I certainly wouldn't assume that debates will always have a similarly noticable impact, perhaps 2010 was the exception. Even if someone does win in the post-debate verdict polls, don't assume it will necessarily make any difference in voting intention - wait for the next regular voting intention polls to see if it's really changed views (a wait that will sadly be extended by the Easter bank holidays, which I expect means this weekend will be light on polls). Certainly don't put too much weight on shifts in the votes of people within the samples of viewers in the debate polls... remember they are made up only of viewers, so will magnify any effect. Most voters won't be watching.

It's possible that all the verdict polls show the same "winner". What do we make of it if they don't? Well, it might just be that the race was very close and normal sample variation has meant different companies show different winners. Given it's a seven way race that seems quite likely to me and if that is the case, the real story shouldn't be that company A shows X winning by one point while company B shows Y winning by one point, it should be the polls showing a draw between X & Y. If there is a big difference between different polls, look at how they are weighting things - there is no "right" way of polling a debate like this, in 2010 some companies weighted to make the sample representative of the country as a whole (perhaps by past vote, perhaps by current voting intention before the debate starts), some companies weighted it to be representative of people watching the debate, which isn't necessarily the same (what if voters from one party are just a lot more likely to watch!).

The debate is 8pm to 10pm, judging by the polls after previous debates, the first results of verdict polls should come out in the ten to fifteen minutes following that. I'll update as they come in.

UPDATE1: As well as their poll at full time which will follow later, ComRes also did a half time poll. Asked who was performing best Nigel Farage came top on 24%, followed very closely by Miliband 21%, Cameron 19% and Sturgeon 18%. Farage was also seen as performing worst - picked by 22%, suggesting he's having quite a polarising effect.

UPDATE2: First of the reaction polls is out from YouGov - Sturgeon clearly ahead on 28%, Farage second 20%, Cameron 18%. Rest to come as soon as they appear.

UPDATE3: ICM have Miliband and Cameron almost neck and neck at the top - Miliband 25%, Cameron 25%. Behind them Farage and Sturgeon are close together for third place - Farage 19%, Sturgeon 17%.

UPDATE4: ComRes have an extremely even split in their results - Cameron 21%, Miliband 21%, Farage 21%, Sturgeon 20%.

UPDATE5: Some more data from ComRes - Nigel Farage was seen as the most honest (26%), Ed Miliband most understanding of your concerns (25%), David Cameron on having the best ideas for Britain's future (27%) and David Cameron most capable of leading the country (40%)