Findings: Strong case for a good plea

A warning to lecturers: do not rest on your laurels. Psychologists have found that an expert with a good reputation will provoke a more hostile response than someone perceived as a non-expert if he or she presents weak arguments, writes Steve Farrar.

While people are often persuaded more by experts than non-experts, researchers noted that the message had to be credible or a backlash was likely to follow.

A team of German psychologists - Gerd Bohner at Universitat Bielefeld, Markus Ruder at Universitat Erfurt, and Hans-Peter Erb at Martin-Luther-Universitat Halle-Wittenberg - gave students at the University of Mannheim a series of presentations and then tested their responses.

Groups of volunteers listened to a man described as an 18-year-old school student who was a member of a Dutch youth group, and a second man who was described as an award-winning professor and director of a renowned institute for ecology and infrastructure who was working for the Dutch government.

Both alternately gave strong, ambiguous or weak arguments in favour of the construction of a tunnel beneath Rotterdam harbour.

The psychologists found that ambiguous arguments were more likely to be well received by the experimental subjects if they were presented by the professor.

Predictably, the opposite reaction greeted the ambiguous argument given by the school student, a person with less expertise.

When the message was strong, a higher perceived level of expertise resulted in a better reception.

But when the arguments were weak, the psychologists detected a strong backlash effect: the volunteers had a far more negative reaction to the professor and his message than to the student.

The psychologists believed this was because the reputation of the expert heightened the students' expectation.

When these were dashed by the presentation of a poor argument, the readers reacted in a hostile fashion.

The findings are published in the British Journal of Social Psychology.