Social Psychology’s Most Underappreciated Theory
Bibb Latané’s theory of social impact explains how we are influenced by others.
Posted May 17, 2026 | Reviewed by Lybi Ma
Are you familiar with Bibb Latané’s theory of social impact, first introduced in 1981? Probably not. Although behavioral scientists have cited his seminal article nearly 5,000 times, the general public is largely unaware of Latané’s major contribution.
Social psychology is the branch of psychology that studies social influence. Advertising , conformity , cults, obedience, propaganda—stuff like that. Latané’s theory deserves our appreciation because it makes precise, testable predictions and can account for (explain) a wide range of social psychological phenomena.
The Theory of Social Impact
Latané said that individuals are influenced by social forces that are similar in some ways to physical forces such as light, gravity, and magnetism. He offered a simple analogy. People who influence a target individual are like lightbulbs casting light on a white surface. The total amount of light falling on the surface is a function of the number of bulbs, the wattage of the bulbs, and the proximity of the bulbs. The level of illumination is very low, for example, when a single 15-watt bulb is 100 feet away from the surface.
According to Latané (1981), the intensity of a social force—its psychological oomph—is the product of the number, strength, and immediacy of impact sources (the light bulbs in his analogy).
This relationship can be expressed in a mathematical equation: Intensity of Social Impact = S x I x N . If S (or I or N) equals 0, then the intensity of impact is zero.
In the diagram, the strength of a source (or target) is represented by the size of its circle. The immediacy of a source is represented by the distance between it and its target.
A single source can impact multiple targets, in which case the source’s overall oomph is split across the targets. This describes the situation in which a single police officer tells a crowd of protestors to disperse. The pressure to comply felt by each protestor is relatively weak.
Latané noted that social influence is not one-sided; it flows in both directions. Therefore, we must clearly specify sources and targets in our analyses. In a classroom, for example, the teacher (source) influences students (targets), but students also influence teachers.
Latané said the social impact of “number” increases at a decreasing rate. Adding a second lightbulb in a poorly lit room makes a big difference, but adding a bulb to 20 other bulbs in a well-lit room makes little difference.
Illustrations of the Theory
Here are three examples that illustrate the theory’s ability to help us better understand social psychological phenomena.
A source with high strength exerts more impact than a source with low strength . When I testify as an expert witness, the attorney who has hired me devotes much time to telling the jury about my professional qualifications. The opposing attorney tries to diminish my credibility by asking me how much I am being paid. Both attorneys know a witness will have more impact if jurors see the witness as knowledgeable and trustworthy.
A distant source exerts less impact than a nearby source . Maximum-range killing is the range at which a killer is unable to see or hear his individual victims without using some form of mechanical assistance. Think “dropping bombs from an airplane at 10,000 feet.” According to one military expert, there are no recorded instances in which a soldier has refused to kill the enemy under maximum-range conditions. Killing an enemy soldier who is staring you in the face, however, is psychologically very difficult; some soldiers refuse to do it (Waller, 2002, p. 236).
The social impact of the number increases at a decreasing rate . Some years ago, performers were waiting backstage before appearing in a talent show in front of 2,500 fellow students at Ohio State. Researchers asked the performers to report their degree of anxiety . One performer in a solo act felt, on average, six times more anxious than a performer in an act of 10. Adding one person to an act of one reduced the anxiety by about 75 percent, whereas adding one person to an act of nine had little effect (Jackson and Latané, 1981).
Many Psychology Today readers rightfully admire Festinger’s theory of cognitive dissonance and Bandura’s theory of social learning . Please add one more to the list of social psychological theories worthy of admiration.
Jackson, J. M., & Latané, B. (1981). All alone in front of all those people: Stage fright as a function of number and type of co-performers and audience. Journal of Personality and Social Psychology , 40 (1), 73-85.
Latané, B. (1981). The psychology of social impact. American Psychologist , 36 (4), 343-356.
Waller, J. (2002) Becoming Evil: How Ordinary People Commit Genocide and Mass Killing . Oxford University Press.
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Lawrence T. White, Ph.D. , is Professor Emeritus of Psychology at Beloit College in Wisconsin.
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This article is part of the Bringwise Psychology Journal — daily insights on human behavior, mental health, and personal growth.