However, ELM itself does not explain why sources, characteristics of messages, and traits of recipients influence attitude changes via persuasive messages. To explain these effects, additional social psychological theories are needed. I will focus on two source factors, namely credibility and attractiveness. Hence, one of your first goals in developing a powerful persuasive message should be the selection of a credible source. However, credibility is not an objective characteristic like gender, hair color, or skin color.
Credibility is a characteristic that has to be inferred by the recipient of the message.
In a way credibility is as much a source effect as a recipient effect because the credibility of a source exists only in the perception of a receiver. However, if many receivers attribute credibility to a single source, one may conclude that credibility is a characteristic of the source and not a characteristic of the receivers. On the other hand, if receivers differ greatly in their perception of credibility of the same source, we may infer that this variability reflects individual differences between receivers in their perceptions of credibility. Because credibility is an inference, it can be related to many different cues that people use to infer credibility. However, at a more abstract level, credibility has two major components, which are called expertise and trustworthiness .