20/04/2015 12:02 BST | Updated 20/06/2015 06:59 BST

Five Lessons from the Challengers' Debate

Following the seven-way leaders' debate in Manchester, a fortnight later the focus shifted to a five-way debate between the leaders of the "challenger" parties - the same candidates as previously, minus David Cameron and Nick Clegg. Once again, the Ipsos MORI "worm" returned to pass judgement on each leader's performance.

An audience of 50 politically balanced undecided voters from England, Wales and Scotland watched the debate from the BBC's studios in central London. Their reactions were translated to an on-screen trace - the "worm" - telling us how positive or negative the audience were about the events unfolding on-screen.

So what immediately stood out during the debate? We've identified five emerging talking points:

1. As talking about the NHS was popular in the first debate, talking about housing was a big winner this time around. We know that it is an important issue for the public - three quarters of whom say there is a housing crisis in this country - and this was reflected in the worm's reaction. There were consistently positive reactions when candidates discussed plans to build more houses.

2. The discussion about helping vulnerable groups was also popular with the worm. Talking about plans for helping former servicemen and women, especially veterans of overseas conflicts, allowed each candidate a chance to shine. Similarly, our audience reacted enthusiastically when candidates addressed concerns around social and elderly care.

3. The final question from the debate audience - about each party's "red lines" when negotiating a post-election coalition government - proved very popular with the worm. Clearly, our audience saw the composition of the next government as a pressing issue. However, judging by the tepid response from the worm, no candidate's answer to the question was thoroughly convincing.

4. Those candidates not present on stage were not forgotten. Initially, the worm approved when the absence of the Prime Minister was highlighted and our social media analysis showed this too. Our undecided audience wanted to see Cameron and Clegg take part, though they soon tired of such negativity.

5. There was a lot of "churn" underneath the average worm figure seen on-screen. Reflecting the leaders' desire to concentrate on their positive messages, the average score was more positive than negative. However, a large minority of the individual button presses were negative. Of the roughly 22,000 total button presses during the debate, around 30% were negative, while around half were positive, suggesting a range of different views across our audience.

Ultimately, there were pros and cons for each of the candidates. As in the last debate, and as we observed in 2010, the worm didn't like it when candidates squabbled. And, unsurprisingly, direct criticism of the debate audience was especially unpopular - though the worm was particularly approving of how host David Dimbleby handled the situation. In contrast, appealing to our hopes and idealism struck a chord.

What impact this debate has on public perceptions of the candidates - both present and absent on the night - and how people vote on 7th May remains to be seen. Our latest Political Monitor suggests that while the last seven-way debate may have helped boost some of the leaders' personal ratings, the race between the Conservatives and Labour remains as tight as ever.