The use of so-called "worm" approval graphs in televised election debates can strongly affect the way in which viewers will vote, opening up the possibility of the worm being used unscrupulously to undermine democracy.

The warning on the possible subversive uses of the worm comes from psychology profs in the UK following a study in which they sought to measure the worm's effects on viewers' thinking. The worm is generated by a small group of undecided voters selected by the broadcaster - sometimes as few as 12 - who generate it using handsets to signify approval or disapproval of what a politician is saying.

"Apart from the concerns about unintentional bias, there is real possibility that the worm could be used to systematically bias the outcome of the election," says Professor Jeff Bowers of Bristol uni.

"Given the small sample of undecided voters that generate the worm, just one or two persons could influence the worm by voting for one candidate no matter what. The system is cute, but open to abuse."

Bowers and his colleagues measured the worm's effects by having their study participants watch the third UK election debate, onto which a doctored worm was superimposed. They say that "successfully convinced the majority of the viewers taking part in the study that they were watching an authentic audience response to the live debate".

In the debate seen by one group of 75, the worm was manipulated to favour Gordon Brown: in the other the worm loved Nick Clegg. Apparently this had such an effect on the study participants that it would have translated into significant gains for them on election day.

"We were amazed by the size of the effect that our worms had on viewers' opinions of who won the debate, and even on their choice of preferred Prime Minister. If our results were to generalise to the population at large, a biased worm in a debate shortly before polling day could determine the result of a close election," says Professor Colin Davis of Royal Holloway.

"The squiggly worm is certainly interesting to watch — sometimes more interesting than the candidates — but there's a real danger that we can get sucked in by the worm and allow it to sway, or even determine, our opinion. Results like ours force us to reconsider to what extent 'our' opinions really are our own."

You can read full details of the study here courtesy of the journal PLoS One. ®