person's subjective probability that the behavior produces the outcome in question. A belief is accessible if available from long-term memory. The concept of outcome expectancy originated in the expectancy-value model. Outcome expectancy can be a belief, attitude, opinion, or expectation. According to the theory of planned behavior, an individual's positive evaluation of his or her performance of a particular behavior is similar to the concept to perceived benefits. A positive evaluation refers to a belief regarding the effectiveness of the proposed behavior in reducing the vulnerability to negative outcomes. By contrast, a negative self-evaluation refers to a belief regarding adverse consequences that can result from the enactment of the behavior. Social influence The concept of social influence has been assessed in both the theory of reasoned action and theory of planned behavior. Individuals' elaborative thoughts on subjective norms are perceptions of whether they are expected by their friends, their family, and society in general to perform a particular behavior. Social influence is measured by evaluating the attitudes of social groups. For example, in the case of smoking: Subjective norms the individual attaches to the peer group include thoughts such as, "Most of my friends smoke" or "I feel ashamed of smoking in front of a group of friends who don't smoke"; Subjective norms the individual attaches to the family include thoughts such as, "All of my family smokes, and it seems natural to start smoking" or "My parents were really mad at me when I started smoking"; and Subjective norms the individual attaches to society or the general culture include thoughts such as, "Everyone is against smoking" or "We just assume everyone is a nonsmoker." While most models are conceptualized within individual cognitive space, the theory of planned behavior considers social influence in terms of social norms and normative beliefs. Given that an individual's behavior (e.g., health-related decision-making such as diet, condom use, quitting smoking, and drinking, etc.) might very well be located in and dependent on social networks and organizations (e.g., peer group, family, school, and workplace), social influence has been a welcomed addition to the theory. Model Human behavior is guided by three kinds of considerations: behavioral beliefs, normative beliefs, and control beliefs. In their respective aggregates, behavioral beliefs produce a favorable or unfavorable attitude toward the behavior, normative beliefs result in a subjective norm, and control beliefs pertain to perceived behavioral control. In combination, the attitude toward