Perceived Expertise, Expressed Certainty, and PersuasivenessA recent paper by graduate student Uma R. Karmarkar and professor of marketing Zakary L. Tormala of the Stanford Graduate School of Business looks at an aspect of being persuasive to consumers that in all likelihood has broader applicability.1
Karmarkar and Tormala investigate the effect on persuasiveness of whether someone making a subjective recommendation (e.g., concerning a restaurant) expresses certainty or, alternatively, a degree of uncertainty about the recommendation.
The research indicates that the effect of expressing certainty/uncertainty on persuasiveness when subjective judgments are involved and when the argument presented is strong depends on whether the recommendation comes from a perceived expert or a perceived nonexpert. Specifically,
... low[-]expertise sources violate expectancies, simulate involvement, and promote persuasion when they express certainty, whereas high[-]expertise sources violate expectancies, simulate involvement, and promote persuasion when they express uncertainty.Karmarkar and Tormala reached their conclusion by analyzing the results of three experiments:
- An initial test of the incongruity hypothesis, i.e., the hypothesis that an expert who expresses uncertainty, or a non-expert who expresses certainty, will intrigue message receivers and thereby make them more susceptible to persuasion. The results supported this hypothesis.
- An investigation of the effect of the message deliverer's certainty on persuasion. Karmarkar and Tormala tested the hypotheses that (1) violation of expectations concerning the relation of expertise and certainty increases the message receiver's involvement (attention to and interest in the message), and (2) increased receiver involvement increases the persuasiveness of the message (assuming it includes strong arguments). The results supported these hypotheses.
- An investigation of the impact of varying argument quality. Karmarkar and Tormala tested the hypotheses that (1) increasing receiver involvement by establishing incongruity between the deliver's expertise and certainty has more of an impact on persuasiveness for strong arguments than for weak arguments, and (2) strong arguments produce higher "thought favorability" (e.g., favorable ideas about a restaurant under review), which, in turn, produce more persuasion (in the form of favorable attitudes toward, and interest in, the restaurant). The results supported these hypotheses.
Note that incongruity between expertise and certainty, by increasing receiver involvement, will tend to undermine persuasion if the arguments in the message are weak. At best, there will likely be no effect on the receiver's attitudes and intentions.
- "... individuals lacking in established expertise can augment their persuasive impact when they have strong arguments by strategically incorporating expressions of high certainty into their message."
- "... when experts have strong arguments on their side, they will be more influential if they express uncertainty rather than certainty about their opinion or recommendation."
Note: You can read the Stanford business school's summary of Karmarkar and Tormala's research here.
1 Uma R. Karmarkar and Zakary L. Tormala, "Believe Me, I Have No Idea What I’m Talking About: The Effects of Source Certainty on Consumer Involvement and Persuasion," Journal of Consumer Research, Vol. 36, No. 6 (April 2010); published online October 6, 2009.