Social impact theory was created by Bibb Latané in 1981 and 
consists of four basic rules which consider how individuals can be 
"sources or targets of social influence".
 Social impact is the result of social forces including the strength of 
the source of impact, the immediacy of the event, and the number of 
sources exerting the impact. The more targets of impact that exist, the less impact each individual target has.
Original research
According
 to psychologist Bibb Latané, social impact is defined as any influence 
on individual feelings, thoughts or behavior that is created from the 
real, implied or imagined presence or actions of others. The application
 of social impact varies from diffusion of responsibility to social 
loafing, stage fright or persuasive communication. In 1981, Latané 
developed the social impact theory using three key variables:
- Strength (S) is a net of all individual factors that make a person influential. It covers stable, trans-situational, intrapersonal factors — size, intellect, wealth — as well as dynamic, situation-specific relational components like belonging to the same group.
- Immediacy (I) takes into account how recent the event occurred and whether or not there were other intervening factors
- The number of sources (N) refers to the amount of sources of influence
With these variables, Latané developed three laws through formulas — 
social forces, psychosocial, and multiplication/division of impact.
Social forces
The
 social forces law states that i = f(S * I * N). Impact (i) is a 
function of the three variables multiplied and grows as each variable is
 increased. However, if a variable were to be 0 or significantly low, 
the overall impact would be affected.
Psychosocial law
The
 Psychosocial law states that the most significant difference in social 
impact will occur in the transition from 0 to 1 source and as the number
 of sources increases, this difference will become even eventually. The 
equation Latané uses for this law is
 
That is, some power (t) of the number of people (N) multiplied by the 
scaling constant (s) determines social impact.  Latané applied this 
theory to previous studies done on imitation and conformity as well as 
on embarrassment. Asch's study of conformity in college students 
contradicts the psychosocial law, showing that one or two sources of 
social impact make little difference. However, Gerard, Wilhelmy, and 
Conolley conducted a similar study on conformity sampling from high 
school students. High school students were deemed less likely to be 
resistant to conformity than college students, and thus may be more 
generalizable, in this regard, than Asch's study. Gerard, Wilhelmy, and 
Conolley's study supported the psychosocial law, showing that the first 
few confederates had the greatest impact on conformity.  Latané applied 
his law to imitation as well, using Milgram's gawking experiment. In 
this experiment various numbers of confederates stood on a street corner
 in New York craning and gawking at the sky. The results showed that 
more confederates meant more gawkers, and the change became increasingly
 insignificant as more confederates were present.  In a study Latané and
 Harkins conducted on stage fright and embarrassment, the results also 
followed the psychosocial law showing that more audience members meant 
greater anxiety and that the greatest difference existed between 0 and 1
 audience members.
Multiplication/divisions of impact
The
 third law of social impact states that the strength, immediacy, and 
number of targets play a role in social impact. That is, the more 
strength and immediacy and the greater number of targets in a social 
situation causes the social impact to be divided amongst all of the 
targets. The equation that represents this division is
This law relates to diffusion of responsibility,
 in which individuals feel less accountable as the number of people 
present increases. In emergency situations, the impact of the emergency 
is reduced when more people are present.
The social impact theory is both a generalizable and a specific 
theory. It uses one set of equations, which are applicable to many 
social situations. For example, the psychosocial law can be used to 
predict instances of conformity, imitation and embarrassment. Yet, it is
 also specific because the predictions that it makes are specific and 
can be applied to and observed in the world. The theory is falsifiable 
as well. It makes predictions through the use of equations; however, the
 equations may not be able to accurately predict the outcome of social 
situations. Social impact theory is also useful. It can be used to 
understand which social situations result in the greatest impact and 
which situations present exceptions to the rules. 
While Social Impact theory explores social situations and can 
help predict the outcomes of social situations, it also has some 
shortcomings and questions that are left unresolved. The rules guiding 
the theory depict people as recipients that passively accept social 
impact and do not take into account the social impact that people may 
actively seek out. The model is also static, and does not fully 
compensate for the dynamics involved in social interactions. The theory 
is relatively new and fails to address some pertinent issues. These 
issues include finding more accurate ways to measure social outcomes, 
understanding the "t" exponent in psychosocial law, taking 
susceptibility into account, understanding how short-term consequences 
can develop into chronic consequences, application to group 
interactions, understanding the model's nature (descriptive vs. 
explanatory, generalization vs. theory).
Applying Social Impact Theory
The
 social impact theory specifies the effects of social variables — 
strength, immediacy, and number of sources — but does not explain the 
nature of these influencing processes. There are various factors not 
considered by experimenters while implementing the theory. Concepts such
 as peripheral persuasion affect how communicators may be more credible 
to some individuals and untrustworthy to others. The variables are 
inconsistent from individual to individual, possibly associating 
strength with source credibility and attractiveness or immediacy with 
physical closeness. Therefore, in the application of the social impact 
theory, the idea of persuasiveness, the ability to induce someone with 
an opposing position to change, and supportiveness, the ability to help 
those who agree with someone's point of view to resist the influence of 
others, is introduced. Ultimately, an individual's likelihood of change 
and being influenced is a direct function of strength (persuasiveness), 
immediacy and the number of advocates and is a direct inverse function 
of strength (supportiveness), immediacy and number of target 
individuals.
Subsequent development
The Dynamic Social Impact Theory
 was developed by Latané and his colleagues in 1996. This theory is 
considered an extension of the Social Impact Theory as it uses its basic
 principles, mainly that social influence is determined by the strength,
 immediacy, and number of sources present, to describe how majority and 
minority group members influence one another. As its name suggests, the 
Dynamic Social Impact Theory proposes that groups are complex systems 
that are constantly changing and are never static. Groups that are 
spatially distributed and interact repeatedly organize and reorganize 
themselves in four basic patterns: consolidation, clustering, correlation, and continuing diversity. These patterns allow for group dynamics to operate and ideas to be diffused throughout the group.
- Consolidation – as individuals interact with each other, over time, their actions, attitudes, and opinions become uniform. In this manner, opinions held by the majority of the group spread to the minority, which then decreases in size.
- Clustering – individuals tend to interact with clusters of group members with similar opinions. Clusters are common when group members communicate more frequently with members in close proximity, and less frequently with members who are more distant. Minority group members are often shielded from majority influence due to clustering. Therefore, subgroups can emerge which may possess similar ideas to one another, but hold different beliefs than the majority population.
- Correlation – over time, individual group members` opinions on a variety of issues converge and correlate with each other; this is true even of issues that are not discussed by the group.
- Continuing Diversity – a degree of diversity can exist within a group if minority group members cluster together or minority members who communicate with majority members resist majority influence. However, if the majority is large or minority members are physically isolated from one another, this diversity drops.
Contemporary research
In
 1985 Mullen analyzed two of the factors that Latané associated with 
Social Impact theory. Mullen conducted a meta-analysis that examined the
 validity of the source strength and the source immediacy. The studies 
that were analyzed were sorted by the method of measurement used with 
the self-reported in one category and the behavior measurements in the 
other category. Mullen's results showed that the source strength and 
immediacy were only supported in cases in which tension was 
self-reported, and not when behavior was measured.  He thus concluded 
that Latané's source strength and immediacy were weak and lacked 
consistency. Critics of Mullen's study, however, argue that perhaps not 
enough studies were available or included, which may have skewed his 
results and given him an inaccurate conclusion.
A study conducted by Constantine Sedikides and Jeffrey M. Jackson
 took another look at the role of strength and within social impact 
theory. This study was conducted in a bird house at a zoo. In one 
scenario, an experimenter dressed as a bird keeper walked into the bird 
house and told visitors that leaning on the railing was prohibited. This
 was considered the high-strength scenario because of the authority that
 a zookeeper possesses within a zoo. The other scenario involved an 
experimenter dressed in ordinary clothes addressing the visitors with 
the same message. The results of the study showed that visitors 
responded better to the high-strength scenario, with fewer individuals 
leaning on the railing after the zookeeper had told them not to.  The 
study also tested the effect that immediacy had on social impact. This 
was done by measuring the incidences of leaning on the rail both 
immediately after the message was delivered and at a later point in 
time. The results showed that immediacy played a role in determining 
social impact since there were fewer people leaning on the rails 
immediately after the message. The visitors in the bird house were 
studied as members of the group they came with to determine how number 
of targets would influence the targets' behavior. The group size ranged 
from 1 to 6 and the results showed that those in larger groups were less
 likely to comply with the experimenter's message than those in smaller 
groups. All of these findings support the parameters of Latané's Social 
Impact Theory.
Kipling D. Williams, and Karen B. Williams theorized that social 
impact would vary depending on the underlying motive of compliance. When
 compliance is simply a mechanism to induce the formation of a positive 
impression, stronger sources should produce a greater social impact. 
When it is an internal motive that induces compliance, the strength of 
the source shouldn't matter. Williams and Williams designed a study in 
which two persuasion methods were utilized, one that would evoke 
external motivation and one that would evoke internal motivation. Using 
these techniques, experimenters went from door to door using one of the 
techniques to attempt to collect money for a zoo.  The foot-in-the-door 
technique was utilized to evoke the internal motive. In this technique, 
the experimenter would make an initial request that was relatively 
small, and gradually request larger and larger amounts. This is 
internally motivated because the target's self-perception is altered to 
feel more helpful after the original contribution. The door-in-the-face 
technique, on the other hand, involves the experimenter asking for a 
large amount first; and when the target declines, they ask for a much 
smaller amount as a concession. This technique draws on external 
motivation because the request for a concession makes one feel obliged 
to comply. The experiment was conducted with low-strength and 
high-strength experimenters. Those who were approached by 
higher-strength experimenters were more likely to contribute money. 
Using the different persuasion approaches did not produce statistically 
significant results; however, it did support Williams and Williams 
hypothesis that the strength of the experimenter would heighten the 
effects of the door-in-the-face technique, but have minimal effect on 
the foot-in-the-door technique.
There have also been studies done to examine Latané's dynamic 
social impact theory. One study was conducted within three classrooms. 
Two of these classes were small and one of them was large. The 
experimenter would develop 10 moderate multiple choice questions, which 
were read aloud to the class one at a time. The students were then 
instructed to discuss each question as it was read aloud with their 
neighbors and come to a final answer at the end of the given time 
period. The results of this simple study were able to illustrate and 
support the effects of dynamic social impact theory. The answers were 
consolidated because many of those with a minority answer within their 
group would comply with the majority opinion, which reduced the 
diversity of the answers. There was also considerable clustering: those 
sitting near each other tended to have the same answers. Correlation was
 visible because answers that weren't originally apparently related, 
became connected for students within some of the groups. However, none 
of the answers were entirely eliminated, allowing for continuing 
diversity. Many of the groups had members that changed their answers 
from the wrong answer to the right answer; however, there were also 
students that changed their answer to the wrong one after the 
discussion. 
Due to social media's influence, there has been movement towards 
e-commerce.  Researchers have since looked into the relationship between
 social media influence and visit and purchase intentions within 
individuals.
Most recently, Rodrigo Perez-Vega, Kathryn Waite, and Kevin O'Gorman 
 suggest that the theory is also relevant in the context of social 
media. Empirical research on this context has found support for the 
effects of numbers of sources (i.e. likes) in performance outcomes such 
as box office sales. Furthermore,  Babajide Osatuyi and Katia Passerini operationalized strength, immediacy, and number using Social Network Analysis
 centrality measures, i.e., betweeness, closeness, and degree 
centralities to test two of the rules stipulated in Social Impact 
Theory. They compared the influence of using Twitter and discussion 
board in a learning management system (e.g., Moodle and Blackboard) on 
student performance, measured as final grade in a course. The results 
provide support for the first law, i.e., impact (grade) as a 
multiplicative resultant of strength, immediacy, and number of 
interactions among students. Additional interesting insights were 
observed in this study that educators ought to consider to maximize the 
integration of new social technologies into pedagogy.
