Vested interest is a communication theory that seeks to explain how influences impact behaviors. As defined by William Crano, vested interest refers to the amount that an attitude object is deemed hedonically relevant by the attitude holder (Crano, 1995). In Crano's idea of vested interest, if the attitude object is subjectively important and the perceived personal consequences are significant, there will be a greater chance the individual's attitude will be expressed behaviorally. For example, a 30 year old individual is told that the legal driving age is being raised from 16 to 17 in his state. While he may not agree with this law, he is not impacted like a 15 year old prospective vehicle operator and is unlikely to be involved in protesting the change. This example illustrates the point that highly vested attitudes concerning issues are related to an individual’s situational point of view.

A key factor to consider with vested interest is the level/type of involvement the individual has with a particular attitude object. This can be broken up into three main components. Value-relevant involvement concerns behaviors which support/reinforce values of the individual. Impression-relevant involvement relates to those behaviors which serve to create or maintain a specific image of the individual. This could, in some ways, be compared to a low-self monitor. Outcome-relevant involvement concerns those behaviors which hold direct personal consequences at a premium for the individual and as a result, corresponds most closely to vested interest (Crano, 1995).

Ego-involvement’s main foci are an individual’s attitudes psychologically experienced as being a part of “me”. The more highly emotional people are, minor differences in beliefs can be viewed as significantly large, whereas a person with low ego-involvement offers great latitude before acting. It is important to note that highly vested attitudes can be experienced as ego involving, the opposite isn't always true. An individual can be ego involved in a certain attitude that has no hedonic consequence.

The factor to consider with vested interest and its application towards attitude-consistent actions is attitude importance. Attitude (or issue) importance concerns not only matters of personal consequence, but also those matters of national/international interest (Crano, 1995). While both of these can fall in line with each other, vested interest and attitude importance are not the same. For example, consider the plight of an African nation that has been ravaged by an influenza epidemic. While an individual may view this situation as objectively important, because of the possibly low level of personal consequence (vested interest), his resultant behaviors may not be indicative of his attitude concerning the situation. In other words, since the issue at hand is of little hedonic relevance to the perceiver, the amount of vested interest is low, and is therefore unlikely to produce attitude-consistent actions.

Vested interest is determined by, and must include, all five of these sub-components: stake, salience, certainty, immediacy, and self-efficacy. It can also be argued that distance (both mentally and physically) could potentially be another component of this theory. Oppositional behavior or NIMBY "Not In My Back Yard" (Thornton and Knox, 2002) will be used as an example of how all components are utilized. A new prison was built in Thompson, Illinois, and sparked various actions in and around the community.

Stake refers to the perceived personal consequence of an attitude that is directly related to the intensity of vested interest. In its basic form, the more that is at stake concerning a particular issue, the stronger the attitude will be. Consequently, as attitude strength increases, the consistency of attitude-based actions also increases (Crano, 1995). From the example above, it was well known the prison would create jobs and revenue for the community and a majority of the community supported the decision to house the inmates. Unfortunately, the minority (homeowners by the site) were not happy about the location and most decided they would move if the things pressed on.

Salience refers to the perceiver’s awareness of the effects of an attitude upon himself (Crano, 1995). In other words, the prominence of an issue, as perceived by an individual, shapes the strength of his resulting attitude. Again, the issue of salience was split between supporters and non-supporters. The media consistently pushed the new job message and how it would impact a large region of both Illinois and Iowa. Even though most people would not want a prison in their back yard, the positives outweighed the negatives of those living next to it.

Certainty refers to perceived likelihood of personal consequences as a result of an attitude or action (Crano, 1995). Simply stated, if a certain course of action is taken, then the chances of a specific event occurring as a result of this action are evaluated by the perceiver to help shape his resultant attitudes and behaviors. Certainty can be easily applied to situations in which an individual knowingly takes a calculated risk. Although the chance of a prison escape is minimal, particularly in a maximum security prison, it could occur and crimes against those living close by would increase. The supporters were certain this would not happen and while those living close continually argued their case on the potential dangers.

Immediacy refers to an individual’s perceived amount of time between an action and its resulting consequences (Crano, 1995). Immediacy can be considered an extension of certainty; however, these two entities are completely separate. Opposition to the prison felt the amount of time for the prison to be built and eventual housing of prisoners was not long enough to make a decision and that it was only a matter of time before something negative happened to the local citizens.

Self-efficacy, in vested interest, is the amount that an individual believes that they are capable of performing an action associated with an attitude or advocated position (Crano, 1995). People with high vested interest that was covered by the other four components would need self-efficacy to stand up and protest the location of the new prison. If they believed there was nothing they could do then they would not act on their attitude held and vested interest will not have been attained.

Various studies have been conducted to determine the effects of vested interest on attitude strengths. In one such study, Crano and Sivacek (1982) visited a university and gathered the results of a proposed drinking age referendum in the state of Michigan. The referendum sought to increase the legal drinking age from 18 to 21. The respondents were divided into three categories, which were high vested interest (those who would be significantly impacted immediately as a result of the referendum), low vested interest (those who would be unaffected by the law change at the time of its inception), and moderate vested interest (those who fell between these extremes). Although 80% of the subjects were opposed to the referendum, their respective levels of vested interest clearly indicated that the strength of their attitudes significantly impacted their resultant behaviors. Roughly half of the high vested interest group joined the anti-referendum campaign. However, roughly one-quarter of the moderate vested interest group and one-eighth of the low vested interest group joined the campaign. (Sivacek & Crano, 1982)

In a second study, Sivacek and Crano (1982) visited Michigan State University. In this experiment, subjects were informed that the university was considering the addition of a senior comprehensive examination to the graduate prerequisites. Respondents were given choices to

The respondents were grouped into the same three categories (high, moderate, and low vested interest). The study found that those of the highest levels of vested interest were significantly more inclined to take actions based upon their attitudes concerning the issue; that is, their resultant behaviors (signing the petition, joining the group, pledging multiple hours with the group) occurred much more consistently (and prevalently) than that of the other two vested interest groups. (Sivacek & Crano, 1982)

Another study conducted by Crano sought to prove that vested interest may impact people's belief that a majority of a population will support their attitude on an issue. This bias is known as false-consensus or assumed-consensus effect. Under the guise of a public opinion survey, Crano (1983) created high and low vested interest groups by identifying whether upper or lower classmen would pay a surcharge to subsidise lost funding from the government. The class who was selected to pay the surcharge had a high degree of vested interest while the student body not required to pay exhibited a lower degree of vested interest. The study then determined the participants estimate of what percentage of the student body would support their beliefs regardless of impact. Crano found that vested interest had an impact on assumed consensus and students believed that a majority of the university's population would support their plight even though only half would be affected. (Crano 1995)

Each of these five entities coexist within an individual’s realm of conscious judgment. Any of these entities, if it creates a strong enough attitude, can cause an individual to either adopt or reject an advocated position. All five are considered anytime an individual is presented with a message that attempts to influence or persuade him to adopt a certain position or perform an action. The process of evaluating these entities can range from near instantaneous to several years; at any rate, all five are considered (consciously or subconsciously) before making a decision.