Final answer:
According to McGuire (1985), the effectiveness of a source in persuasive communication is influenced by a combination of familiarity, likability, and similarity, along with the messenger's credibility. All these factors together determine how effectively the message is conveyed and received by the intended audience.
Step-by-step explanation:
When considering the effectiveness of a source according to McGuire (1985), it's essential to acknowledge that various factors contribute to the influential capacity of the source. In the context of persuasive communication, features such as the credibility, familiarity, likability, and physical attractiveness of the speaker have been shown to impact their persuasiveness. Moreover, the similarity factor is crucial, as we tend to form and maintain relationships with individuals who are akin to us in background, attitudes, and lifestyle. Hence, while none of the factors solely mentioned—familiarity, likability, or similarity—disqualify a source from being effective, the synergy of these aspects heavily influences the overall impact of the source.
Consequently, the answer to what is more important to the effectiveness of the source is not restricted to a single factor but is a combination of all: familiarity, likability, and similarity. These qualities, alongside the credibility of the messenger, shape the immediate and long-term impact of persuasion, as they resonate more with the audience, persuading them favorably towards the message being communicated.