Source expertise and persuasion: the effects of perceived opposition or support on message scrutiny.

Compared to nonexperts, expert sources have been considered to elicit more processing of persuasive messages because of expectations that the information is likely to be valid or accurate. However, depending on the position of an advocacy, source expertise could activate other motives that may produce a very different relation from that found in past research. When messages are counterattitudinal (disagreeable), experts should motivate greater processing than nonexpert sources because of expectations that they will likely provide robust opposition to one's existing views. In contrast, when advocacies are proattitudinal (agreeable), nonexpert rather than expert sources should elicit more scrutiny because of perceptions that they will likely provide inadequate support to recipients' current views. Two studies offer evidence consistent with these predictions. Manipulations of source expertise created different expectations regarding the strength of opposition or support, and these perceptions accounted for effects of source expertise on the amount of message scrutiny.