A worm could turn the close fight for the US presidency

LAST night, Barack Obama and Mitt Romney met for the third and final US presidential debate before November’s elections. The latest polls suggest the race is a lot closer than many expected – not least because Romney was judged to have won the first debate in Denver.

Research on the psychology of elections underlines the importance both of winning debates and of being perceived as the favourite. There is a bandwagon effect – undecided voters gravitate towards the leading candidate. This is social influence and it’s not unlike how we find jokes funnier when we hear other people laughing.

When faced with a complex judgement, it makes sense that we take into account other people’s views. But we also consider the source of information. To some extent, we discount information if we perceive bias. This makes us less vulnerable to political spin.

But spin is not the only form of social influence we’re subjected to. Other forms are more subtle, and potentially harder to resist. A good example is the “worm” – the squiggly line that accompanies televised debates. It’s meant to represent the views of undecided voters, moving up when a candidate says something they endorse, and down when he or she says something they don’t like.

The worm featured during ITV’s coverage of the leaders’ debates during the last UK election. It’s attracted controversy in Australia and New Zealand, with some candidates arguing that the worm was rigged against them. Even without deliberate bias it’s unlikely that the worm accurately represents the views of undecided voters, since it’s based on such a small sample (just 20 people in the case of ITV’s worm.)

In a paper published last year, my colleague and I reported evidence that the worm influences viewers. We asked 150 people to watch the live broadcast of the final UK election debate – a version that included the worm – and then answer a few questions. Unknown to the participants, the worm they saw was manipulated by us. One group saw a worm biased in favour of Gordon Brown, while for another group it favoured Nick Clegg. Although the debate was identical, the group that saw a worm favouring Gordon Brown thought he won the debate, while the group that saw the worm favouring Nick Clegg overwhelmingly thought he was the winner. More worryingly, we saw a similar effect when we asked about their choice of preferred Prime Minister. If people voted immediately after the debate, our manipulation could have had a significant effect.

As the US prepares to choose its next President, it’s concerning that CNN is continuing with the experiment of the worm. Millions of voters are watching debate coverage, and are thus exposed to social influence processes that we know can be very powerful. If the election result turns out to be as close as polls suggest, it will be difficult to rule out the possibility that the deciding vote was cast by the worm.

Colin Davis is professor of cognitive science at Royal Holloway, University of London.