Social Impact Theory

Social Impact Theory Definition

Social Impact TheorySocial impact theory proposes that the amount of influence a person experiences in group settings depends on (a) strength (power or social status) of the group, (b) immediacy (physical or psychological distance) of the group, and (c) the number of people in the group exerting the social influence (i.e., number of sources). Thus, a group that has many members (rather than few members), high power (rather than low power), and close proximity (rather than distant proximity) should exert the most influence on an individual. Conversely, if the strength of the person exposed to the social influence (i.e., target) increases, the immediacy of the group decreases, or if the number of targets increases, the amount of influence exerted by the group on the individual decreases. The theory therefore has direct applications to persuasion and obedience.

Social impact theory differs from other models of social influence by incorporating strength and immediacy, instead of relying exclusively on the number of sources. Although criticisms have been raised, the theory was (and continues to be) important for the study of group influence. Reformulating social impact theory to accommodate the influence of targets on sources (i.e., dynamic social impact theory) has further increased its validity and range of explainable phenomena. Furthermore, pushing social impact theory into applied areas in social psychology continues to offer fresh perspectives and predictions about group influence.

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Tests of Social Impact Theory

Number of Sources

Social impact theory predicts multiple sources will have more influence on a target than will a single source. Research has generally supported this prediction: Many studies have shown a message presented by multiple people exerts more influence than does the same message presented by a single person. However, the effect of multiple sources only holds true under three conditions. First, the influencing message must contain strong (rather than weak) arguments. Weakly reasoned arguments, whether given by multiple sources or not, result in little attitude change. Second, the target must perceive the multiple sources to be independent of one another. The effect of multiple sources disappears if the target believes the sources “share a single brain.” The colluding party will in such cases be no more effective than will a single source. Third, as the number of sources grows large, adding additional sources will have no additional effect. For example, the effect of 4 independent sources substantially differs from the effect of 1 source, but the effect of 12 independent sources does not substantially differ from the effect of 15 independent sources.

Strength and Immediacy

The inclusion of strength and immediacy as variables is unique to social impact theory; no other social influence theory includes these variables. Defining strength and immediacy in research studies is less straightforward than is defining the number of sources, but the operational definitions have been relatively consistent across studies. Researchers usually vary the source’s strength with differences in either age or occupation (adults with prestigious jobs presumably have more strength than do young adult college students). Researchers usually vary the source’s immediacy either with differences in the physical distance between the source and the target (less distance means more immediacy) or, in cases of media presentation, with differences in the size of the visual image of the source (a larger image focused more on the face relative to the body means more immediacy).

Surprisingly, however, these two components of the model have received considerably less empirical investigation than has the number of sources; therefore, the effects of strength and immediacy on influence are less clear. A statistical technique called meta-analysis, which allows researchers to combine the results of many different studies together, has helped researchers draw at least some conclusions. Across studies, meta-analyses on these two variables indicate statistically significant effects of low magnitude (i.e., the effects, though definitely present, are not very strong). Furthermore, strength and immediacy appear to only exert influence in studies using self-report measures; the effects of strength and immediacy wane when more objective measures of behavior are examined.

Dynamic Social Impact Theory

In its traditional form, social impact theory predicts how sources will influence a target, but neglects how the target may influence the sources. Dynamic social impact theory considers this reciprocal relationship. The theory predicts people’s personal attitudes, behaviors, and perceptions will tend to cluster together at the group level; this group-level clustering depends on the strength, immediacy, and number of social influence sources. Day-to-day interaction with others leads to attitude change in the individual, which then helps contribute to the pattern of beliefs at the group level. In support of the immediacy component of dynamic social impact theory, for example, studies have shown randomly assigned participants were much more likely to share opinions and behaviors with those situated close to them than with those situated away from them, an effect which occurred after only five rounds of discussion.

New Directions for Social Impact Theory

Recently, researchers have pushed social impact theory outside the areas of persuasion and obedience into more applied areas of social psychology. For example, recent studies have examined social impact theory in the context of consumer behavior. In one study, researchers varied the size and proximity of a social presence in retail stores, and examined how this presence influenced shopping behavior. Furthermore, several tenets of social impact theory seem to predict political participation. One study found as the number of people eligible to vote increases, the proportion of people who actually vote asymptotically decreases. This finding accords with social impact theory, which predicts an increasingly marginal impact of sources as their number grows very large.

Social impact theory has enjoyed great theoretical and empirical attention, and it continues to inspire interesting scientific investigation.


  1. Harkins, S. G., & Latane, B. (1998). Population and political participation: A social impact analysis of voter responsibility. Group Dynamics: Theory, Research, and Practice, 2, 192-207.
  2. Latane, B., & Wolf, S. (1981). The social impact of majorities and minorities. Psychological Review, 88, 438-453.