Self-monitoring is a theory that deals with the phenomena of expressive controls. Human beings generally differ in substantial ways in their abilities and desires to engage in expressive controls (see dramaturgy). People concerned with their expressive self-presentation (see impression management) tend to closely monitor their audience in order to ensure appropriate or desired public appearances. Self-monitorers try to understand how individuals and groups will perceive their actions. Some personality types commonly act spontaneously and others are more apt to purposely control and consciously adjust their behavior. Self-monitoring is defined as a personality trait that refers to an ability to regulate behavior to accommodate social situations. People who closely monitor themselves are categorized as high self-monitors and often behave in a manner that is highly responsive to social cues and their situational context. High self-monitors can be thought of as social pragmatists who project images in an attempt to impress others and receive positive feedback. Conversely, low self-monitors do not participate, to the same degree, in expressive control and do not share similar concern for situational appropriateness. Low self-monitors tend to exhibit expressive controls congruent with their own internal states; i.e. beliefs, attitudes, and dispositions regardless of social circumstance. Low self-monitors are often less observant of social context and consider expressing a self-presentation dissimilar from their internal states as a falsehood and undesirable.People who are unwilling to self-monitor and adjust their behavior accordingly are often aggressive, uncompromising, and insistent with others. This may make them more prone to condemnation, rejection, and the possible consequent feelings of anger, anxiety, guilt, low self-concept, isolation, and depression. Even the occasional indiscretion can make social situations very awkward, and could result in the loss of a friend, co-worker, client, or even job. Those who are willing to adjust their behavior will often find that others are more receptive, pleasant, and benevolent towards them.
During the 1970s when the self-monitoring concept was introduced it became part of two larger ongoing debates. Within personality research there was the tension between traits and situation; one could think of this as the nature versus nurture debate. Were people more inclined to behave consistent with innate personality traits or were they shaped by their environment? The self-monitoring construct offered a resolution to this debate because there was no need to argue that humans needed to fit entirely into the nature or nurture paradigm. High self-monitors were better predicted by their environment (situation/nurture) while low self-monitors were better predicted by their traits (traits/nature). Another debate that was raging during this time period within social psychology was whether or not attitudes were good predictors of behavior. The self-monitoring construct offered a resolution to this debate as well because it posited that low self-monitors would behave largely consistent with their attitudes, while attitudes would be poor predictors of behavior for high self-monitors. The self-monitoring construct fit neatly into the arguments of the day where high self-monitors affirmed the situation-oriented view typically associated with social psychology, while the low self-monitors affirmed the trait-oriented view typically associated with personality psychology.
Mark Snyder originally developed a scale to measure whether people were high or low self monitors in 1974 as a 25-item measure. In his original study he found that Stanford University students scored significantly higher on the scale than did psychiatric inpatients, but significantly lower than people in the acting profession. The scale was revised into an 18-item measure that is considered psychometrically superior to the original scale and has been used extensively in self-monitoring studies. There has developed great debate over whether or not the self-monitoring scale is a unitary phenomenon. During the 1980s, factor analysis postulated that the self-monitoring scale was actually measuring several distinct dimensions. The three-factor solution was the most common and usually interpreted as Acting, Extraversion, and Other-Directedness (see willingness to communicate). There has developed consensus about the multifactorial nature of the items on the self-monitoring scale; however, there remains differing interpretations about whether or not that jeopardizes the validity of the self-monitoring concept.
A score of 0-8 on Snyder's scale indicates low self-monitoring, while a score of 13-25 indicates high self-monitoring. Some traits of high self-monitors include readily and easily modifying their behavior in response to the demands of the situation, whereas low self-monitors care little about modifying their behavior in response to the situation and tend to maintain the same opinions and attitudes regardless of the situation. High self-monitors find it much easier to modify their behavior based on the situation than low self-monitors do. High self-monitors would be more likely to change their beliefs and opinions depending on who they're talking to, while low self-monitors would tend to be consistent throughout all situations. This has been studied mainly in correspondence with relationships. Compared to Low self-monitors, High self-monitors will have more dating and sexual partners, are more interested in having sex with people they are not in love with, and are more likely to have had sex with someone only once, as well as be more likely to deceive potential romantic partners. High self-monitors are more likely to choose a romantic partner who is attractive but unsociable, while low self-monitors are more likely to choose a partner who is unattractive but sociable.  High self-monitors are also more likely to take on leadership positions than low self-monitors. 
Self-Monitoring in Individualist/Collectivist cultures
Gudykunst et al, (1987) argued that individualism should influence self-monitoring. Cultures high on individualism focus on the self, not others. In individualistic cultures, knowing the context is not necessary to predict others' behavior, thus people from individualistic cultures are more likely to be low self-monitors. Cultures low on individualism (i.e., collectivist cultures), in contrast, value conformity to ingroups and group memberships. In collectivistic cultures, knowing the context and social status of the other person is essential to predicting his or her behavior, thus people from collectivistic cultures are more likely to be high self-monitors. 
There are several theories within social psychology that are closely related to the self-monitoring construct. Icek Ajzen argues that subjective norms are an important antecedent to determining behavioral intention in the Theory of Reasoned Action/Theory of Planned Behavior. High self-monitors tend to weigh subjective norms more heavily than low self-monitors. Studies that evaluate private attitudes and public actions include Ajzen, Timko & White, 1982; and DeBono & Omoto, 1993. Informational cascades theory is related to observation learning theory which was developed by Bikhchandani, S.; Hirshleifer, D. & Welch, I. (1992) and describes how people will follow, sometimes blindly, the actions of others. The self-monitoring construct would identify that high self-monitors may be more susceptible to informational cascades and herd mentality. This can be a problem if a culture of Groupthink is part of the organizations decision making process. High self-monitors are more motivated to attain high social status than low self-monitors. Research drawing on the Elaboration Likelihood Model suggests that high self-monitors, more than low self-monitors, react favorably to peripheral processing of advertising images consistent with high social status.
Self-monitoring is useful for students from preschool to adulthood and can be taught to individuals at a variety of levels of cognitive functioning. Self-monitoring interventions foster independent functioning, which allows individuals with disabilities to rely less on prompts from others (Koegel, Koegel, Harrower, & Carter, 1999). Self-monitoring interventions are among the most flexible, useful, and effective strategies for students with academic and behavioral difficulties (Mitchum, Young, West, & Benyo, 2001). They have demonstrated efficacy for targeting a range of academic abilities (Rock, 2005), self- help skills (Pierce & Schreibman, 1994), behavioral problems (Todd, Horner, & Sugai, 1999), and social behaviors (Strain & Kohler, 1994). Students with behavioral and academic difficulties typically have limited awareness and understanding of their own behavior and its effects on others. Self-monitoring interventions equip students to recognize and keep track of their own behavior (Hoff & DuPaul, 1998; Rhode, Morgan, & Young, 1983). Using these strategies, students can learn to identify and increase positive, pro-social behaviors, the behaviors necessary for success in general education settings. Self-monitoring strategies are individualized plans used to increase independent functioning in academic, behavioral, self-help, and social areas. Rather than focusing on reducing a student’s undesired behavior, self-monitoring strategies develop skills that lead to an increase in appropriate behavior. When self-monitoring skills increase, corresponding reductions in undesired behaviors often occur, even without direct intervention (Dunlap, Clarke, Jackson, Wright, 1995; Koegel, Koegel, Harrower, & Carter, 1999). This collateral behavior change allows teachers and parents to address multiple behaviors with one efficient intervention. The five steps involved in planning a self-monitoring intervention: 1. Identify the target behavior. 2. Select/design a self-monitoring system. 3. Choose reinforcers and how the student will earn them. 4. Teach the student to use the system. 5. Fade the role of the adult in the intervention.
Select the Self-Monitoring Systems
To fit seamlessly into a classroom, home, or work setting, self-monitoring interventions may be structured in a variety of ways. The design of the self-monitoring device is largely determined by the student’s needs and setting in which the intervention will occur. Checklists and charts are common materials used to record behavior.
- Snyder, 1974
- Snyder & Gangestad, 2002
- Wicker, 1969
- Lennox & Wolfe, 1984
- Briggs, Cheek, & Buss, 1980
- Riggio & Friedman, 1982
- Hosch & Marchioni, 1986
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- Snyder, Berscheid & Glick, 1985
- Eby, Cader & Noble, 2003
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- Ajzen, 1985
- Rose, P.; Kim, J. (2011). "Self-Monitoring, Opinion Leadership and Opinion Seeking: a Sociomotivational Approach". Current Psychology 30: 203–214. doi:10.1007/s12144-011-9114-1.
- Snyder & DeBono, 1985
- DeBono & Packer, 1991
- Shavitt, Lowrey, & Han, 1992
- Ajzen, Icek. (1985). From intention to actions: A theory of planned behavior. In J. Kuhl & J. Beckman (Eds.) Action-control: From Cognition to Behavior. Heidelberg, GE: Springer, 11–39.
- Ajzen, I.; Timko, C. & White, J.B. (1982). Self-monitoring and the attitude-behavior relation. Journal of Personality and Social Psychology, 42, 426–35.
- Bikhchandani, S.; Hirshleifer, D. & Welch, I. (1992), A Theory of Fads, Fashion, Custom, and Cultural Change as Informational Cascades. Journal of Political Economy, Vol. 100, No. 5, 992–1026.
- Briggs, S.R.; Cheek, J.M. & Buss, A.H. (1980). An analysis of the Self-Monitoring Scale. Journal of Personality and Social Psychology, 38, 679–86.
- DeBono, K.G. & Omoto, A.M. (1993). Individual differences in predicting behavioral intentions from attitude and subjective norm. Journal of Social Psychology, 133, 825–31.
- DeBono, K.G. & Packer, M. (1991). The effects of advertising appeal on perceptions of product quality. Personality and Social Psychology Bulletin, 17, 194–200.
- Eby, L. T., Cader, J., & Noble, C. L. (2003). Why do high self-monitors emerge as leaders in small groups? A comparative analysis of the behaviors of high versus low self-monitors. Journal Of Applied Social Psychology, 33(7), 1457-1479. doi:10.1111/j.1559-1816.2003.tb01958.x
- Hosch, H.M. & Marchioni, P.M. (1986). The Self-Monitoring Scale: A factorial comparison among Mexicans, Mexican Americans and Anglo Americans. Hispanic Journal of Behavioral Sciences, 8, 225–42.
- Lennox, R. & Wolfe, R. (1984). Revision of the Self-Monitoring Scale. Journal of Personality and Social Psychology, 46, 1349–64.
- Riggio, R.E. & Friedman, H.S. (1982). The interrelationships of self-monitoring factors, personality traits, and nonverbal skills. Journal of Nonverbal Behavior, 7, 33–45.
- Rose, P. & Kim, J. (2011). Self-Monitoring, opinion leadership and opinion seeking: A sociomotivational approach. Current Psychology, 30, 203-214.
- Shavitt, S.; Lowrey, T.M. & Han, S.P. (1992). Attitude functions in advertising: The interactive role of products and self-monitoring. Journal of Consumer Psychology, 1, 337–64.
- Snyder, M. (1974). Self-monitoring of expressive behavior. Journal of Personality and Social Psychology, 30, 526–37.
- Snyder, M., Berschedi, E., & Glick, P. (1985). Focusing on the exterior and the interior: Two Investigations of the initiation of personal relationships. Journal of Personality and Social Psychology, 48, 1427-1439
- Snyder, M. & DeBono, K.G. (1985) Appeals to image and claims about quality: Understanding the psychology of advertising. Journal of Personality and Social Psychology, 49, 586–97.
- Snyder, M. & Gangestad, S. (2000). Self-monitoring: Appraisal and reappraisal. Psychological Bulletin, Vol. 126, No. 4, 530–55.
- Wicker, A.W. (1969). Attitudes versus actions: The relationship of verbal and overt behavioral responses to attitude objects. Journal of Social Issues, 25, 41–7.
- Mark Snyder's Faculty Web Page at The University of Minnesota
- Self-monitoring scale (Snyder, 1974), online implementation.