Elaboration likelihood model
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The Elaboration Likelihood Model (ELM) of persuasion  is a dual process theory of how attitudes are formed and changed, which was developed by Richard E. Petty and John Cacioppo during the early 1980s. The model examines how an argument's position on the "elaboration continuum", from processing and evaluating (high elaboration) to peripheral issues such as source expertise or attractiveness (low elaboration), shapes its persuasiveness. ELM resembles the heuristic-systematic model of information processing developed about the same time by Shelly Chaiken.
The model defines two processing routes: central and peripheral.
The central path is used when the receiving person cares about the issue at hand and is able to understand it without allowing themselves to be distracted by superficial information. The central path is more likely to leave a lasting persuasion on the receivers if the subject is sympathetic by them. If, however, the receivers of the message are unfavourably inclined towards it, then a boomerang effect (an opposite effect) is likely to occur.
The peripheral path is used when the receiver has little or no interest for the subject. In which case the message conveys peripheral hints to something that the chosen audience may already have a positive attitude towards. These hints can be targeted towards something as simple as pleasurable leisure activities or to something much more complex such as presenting the issue after several other positions to which the receiver is negatively inclined. The person maintains their initial attitude towards the matter if the peripheral signals are not accepted, if they are accepted, however, the person will temporarily change their attitude towards it. This attitude switch may lead to a permanent opinion change, however, this is less likely to happen than a decision made using the central route.
Choice of route
The factors most influencing the route an individual will take in a persuasive situation are motivation (a desire to process the message; see Petty and Cacioppo, 1979) and ability (the capability for critical evaluation; see Petty, Wells and Brock, 1976). The route taken is determined by the extent of elaboration, in turn determined by: attitude, motivation and ability factors. An attitude is a general evaluation, indicating how a person perceives themselves in relation to their surroundings. Attitudes may be influenced by peripheral cues providing guidance or implications, which cause the audience to draw a conclusion and believe it is their own idea. Motivation includes the relevance of the message and a person's "need for cognition" (their enjoyment of thinking through ideas). Motivation is personal to each person and can vary depending on the topic e.g. Students under 21 who drive would be more motivated to get involved and learn about laws that affect them, more than students who are over 21 because the law will not apply to them, so they are not motivated to think about the issue. Ability includes the availability of cognitive resources (e.g., the presence or absence of time pressures or distractions) and the relevant knowledge needed to examine the arguments. Distractions (for example, a persuader trying to convey a message in a room full of crying babies) can affect the ability to process a message. Many evaluations are based on cognitive intelligence, behaviour and guidance. With an understanding of an individual's attitudes, the elaboration may be tailored to the situation. There are two types of elaboration: biased and objective. Elaboration may have positive or negative results, depending on the audience. Individuals with preconceptions about a topic are more difficult to persuade than those who examine the facts.
The advantages of peripheral route thinking is that you can save; time, energy and mental capacity. However this could mean that some information can be overlooked and lead to costly mistakes, mistakes that could have been prevented. The advantages of central route thinking is opposite, costly mistakes can be avoided because you look at all the information, process it and then make your decision. However this does use up lots of; time, energy and mental capacity.
In designing a test for the model, it is necessary to determine if an argument is viewed as strong or weak. If the argument is not seen as strong, the results of persuasion will be inconsistent. A strong argument is defined by Petty and Cacioppo as "one containing arguments such that when subjects are instructed to think about the message, the thoughts they generate are fundamentally favorable". An argument universally viewed as weak will elicit unfavorable results if the subject considers it logically (the central route); a strong argument, under similar circumstances, will return favorable results. Test arguments must be rated by ease of understanding, complexity and familiarity. To study either route of the elaboration likelihood model, the arguments must be designed for consistent results.
Predictions and features
The ELM makes several proposals. Attitudes formed under high elaboration (the central route) are stronger than those formed under low elaboration, making this level of persuasion stable and less susceptible to counter-persuasion. Attitudes formed under low elaboration (the peripheral route) are more likely to cause short-term attitude change.
Variables in ELM routes can serve multiple roles in a persuasive setting, depending on other contextual factors. Under high elaboration, a given variable (e.g. expertise) can serve as an argument ("If Einstein agrees with the theory of relativity, then this is a strong reason for me to as well") or a biasing factor ("if an expert agrees with this position it is probably good, so let me see what else agrees with this conclusion", at the expense of contradicting information.
Under low-elaboration conditions, a variable may act as a peripheral cue (for example, the belief that "experts are always right"). While this is similar to the Einstein example above, this is a shortcut which (unlike the Einstein example) does not require thought. Under moderate elaboration, a variable may direct the extent of information processing: "If an expert agrees with this position, I should really listen to what (s)he has to say".
A variable's effect on elaboration may increase (or decrease) persuasion, depending on the strength of the argument. If the argument is strong, enhancing elaboration will enhance persuasion; if weak, thought will undermine persuasion.
Recent adaptations of the ELM  have added an additional role for variables: to affect the extent to which a person trusts their thoughts in response to a message (self-validation role). A person may feel "if an expert presented this information, it is probably correct, and thus I can trust that my reactions to it are informative with respect to my attitude". This role, because of its metacognitive nature, only occurs in high-elaboration conditions.
- Attitude change
- Need for cognition
- Cognitive biases
- Heuristic-Systematic Model
- Extended transportation-imagery model
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