Source credibility and syllogistic reasoning.

Two experiments examined whether a source credibility effect would be observed for a syllogistic reasoning task. In the experiments, people were given two statements, presented as the results from a survey, followed by a conclusion that was supposedly made by one of two sources. In Experiment 1, one of the sources was described as honest and the other as dishonest, and in Experiment 2, one of the sources was described as an expert and the other as a non-expert. Because a pilot experiment showed that credibility can be overridden by people's experience with a source, all conclusions in Experiments 1 and 2 were ones that were likely to be accepted (i.e., necessary and possible strong conclusions). Both experiments showed a clear source credibility effect, particularly for the invalid conclusions. These results, along with the belief bias effect and previous research with conditional reasoning, suggest that people can be influenced by extraneous context, such as the honesty or expertise of a source, in a syllogistic reasoning task.