If in doubt, shout

Are the most driven evangelists those who are most certain of what they believe, or most uncertain? New research investigates how having our beliefs undermined can make us more determined to convince others.

The starting point is the 1950s work of Leon Festinger, who infiltrated a non-proselytizing UFO cult which believed the world would end on 21 December 1954. When it failed to do so, they decided they had saved the world and became fervently evangelistic.

'If more and more people can be persuaded the belief is correct,' explained Festinger, 'then clearly, it must after all be correct'.

Now for the first time Festinger's theory has been clinically tested, by David Gal and Derek Rucker of Northwestern University, Illinois. They used standard ways of inducing doubt in volunteers - getting them to recall times when they felt plagued with doubt, and asking them to write with the wrong hand.

They asked them to write about their opinions on vegetarianism, or animal testing, or whether Macs are better than PCs. They found, as expected, that those made to feel self-doubt wrote at greater length and spent more time on it than others.

But they also found that the effect only worked if they felt they were talking to someone receptive, and was annulled if their sense of identity was bolstered by talking about their favourite books.

Gal and Rucker's 'If In Doubt, Shout' was published in Psychological Science for November.