The Moderating Impact of Quantitative Information on the Relationship Between Source Credibility and Persuasion: A Persuasion Knowledge Model Interpretation

An experiment manipulated source expertise, source bias, and message format. The findings reveal that expert sources are expected to quantify message claims whereas non-expert sources are not. Persuasion is greater when these expectations are met versus when the source and the message format are incongruent, but only when the source also has self-interest in the advocacy. It appears that source-message incongruity and source bias focus attention on the source and, in combination, lead to negative inferences about the source's manipulative intent. This interpretation is consistent with the Persuasion Knowledge Model (Friestad and Wright 1994).