In social psychology, group polarization refers to the tendency for groups to make decisions that are more extreme than the initial inclination of its members. These more extreme decisions are towards greater risk if individuals' initial tendencies are to be risky and towards greater caution if individuals' initial tendencies are to be cautious. The phenomenon also holds that a group's attitude toward a situation may change in the sense that the individuals' initial attitudes have strengthened and intensified after group discussion.
Group polarization is the phenomenon that when placed in group situations, people will make decisions and form opinions to more of an extreme than when they are in individual situations. The phenomenon has shown that after participating in a discussion group, members tend to advocate more extreme positions and call for riskier courses of action than individuals who did not participate in any such discussion. This phenomenon was originally coined risky shift but was found to apply to more than risk, so the replacement term choice shift has been suggested.
The importance of group polarization is significant as it helps explain group behavior in a variety of real-life situations. Examples of these situations include public policy, terrorism, college life, and violence. For instance, group polarization can largely be seen at political conventions which are broadcasted nation wide before a large election. Generally, a political party holds the same ideals and fundamentals. At times, however, individual members of the party may waver on where they stand on smaller subjects. During a political convention, the political party as a group is strongly united in one location and is exposed to many persuasive speakers. As a result, each individual in the political party leaves more energized and steadfast on where the party as a whole stands with regards to all subjects and behind all candidates, even if they were wavering on where they stood before hand. The phenomenon is also largely observed in the decision-making of a jury, particularly when considering punitive damages in a civil trial. Studies have shown that after deliberating together, mock jury members often decided on punitive damage awards that were either larger or smaller than the amount any individual juror had favored prior to deliberation. The studies indicated that when the jurors favored a relatively low award, discussion would lead to an even more lenient result, while if the jury was inclined to impose a stiff penalty, discussion would make it even harsher. Moreover, in recent years, the Internet and online social media have also presented opportunities to observe group polarization and compile new research. Psychologists have found that social media outlets such as Facebook and Twitter demonstrate that group polarization can occur even when a group is not physically together. As long as the group of individuals begins with the same fundamental opinion on the topic and a consistent dialogue is kept going, group polarization can be observed.
History and origins
The study of group polarization can be traced back to an unpublished 1961 Master’s thesis by MIT student James Stoner, who observed the so-called "risky shift". The concept of risky shift maintains that a group’s decisions are riskier than the average of the individual decisions of members before the group met.
In early studies, the risky-shift phenomenon was measured using a scale known as the Choice-Dilemmas Questionnaire. This measure required participants to consider a hypothetical scenario in which an individual is faced with a dilemma and must make a choice to resolve the issue at hand. Participants were then asked to estimate the probability that a certain choice would be of benefit or risk to the individual being discussed. Consider the following example:
“Mr. A, an electrical engineer, who is married and has one child, has been working for a large electronics corporation since graduating from college five years ago. He is assured of a lifetime job with a modest, though adequate, salary and liberal pension benefits upon retirement. On the other hand, it is very unlikely that his salary will increase much before he retires. While attending a convention, Mr. A is offered a job with a small, newly founded company which has a highly uncertain future. The new job would pay more to start and would offer the possibility of a share in the owner- ship if the company survived the competition of the larger firms.” Participants were then asked to imagine that they were advising Mr. A. They would then be provided with a series of probabilities that indicate whether the new company that offered him a position is financially stable. It would read as following
“Please check the lowest probability that you would consider acceptable to make it worthwhile for Mr. A to take the new job.”
____The chances are 1 in 10 that the company will prove financially sound.
____The chances are 3 in 10 that the company will prove financially sound.
____The chances are 5 in 10 that the company will prove financially sound.
____The chances are 7 in 10 that the company will prove financially sound.
____The chances are 9 in 10 that the company will prove financially sound.
____Place a check here if you think Mr. A should not take the new job no matter what the probabilities.
Individuals completed the questionnaire and made their decisions independently of others. Later, they would be asked to join a group to reassess their choices. Indicated by shifts in the mean value, initial studies using this method revealed that group decisions tended to be relatively riskier than those that were made by individuals. This tendency also occurred when individual judgments were collected after the group discussion and even when the individual post-discussion measures were delayed two to six weeks.
The discovery of the risky shift was considered surprising and counter-intuitive, especially since earlier work in the 1920s and 1930s by Allport and other researchers suggested that individuals made more extreme decisions than did groups, leading to the expectation that groups would make decisions that would conform to the average risk level of its members. The seemingly counter-intuitive findings of Stoner led to a spurt of research around the risky shift, which was originally thought to be a special case exception to the standard decision-making practice. Many people had concluded that people in a group setting would make decisions based on what they assumed to be the overall risk level of a group; because Stoner’s work did not necessarily address this specific theme, and because it does seem to contrast Stoner’s initial definition of risky shift, additional controversy arose leading researchers to further examine the topic. By the late 1960s, however, it had become clear that the risky shift was just one type of many attitudes that became more extreme in groups, leading Moscovici and Zavalloni to term the overall phenomenon "group polarization".
Subsequently, a decade-long period of examination of the applicability of group polarization to a number of fields in both lab and field settings began. There is a substantial amount of empirical evidence demonstrating the phenomenon of group polarization. Group polarization has been widely considered as a fundamental group decision-making process and was well established, but remained non-obvious and puzzling because its mechanisms were not fully understood.
Major theoretical approaches
Almost as soon as the phenomenon of group polarization was discovered, a number of theories were offered to help explain and account for it. These explanations were gradually narrowed down and grouped together until two primary mechanisms remained, social comparison and informational influence.
Social comparison theory
The social comparison theory, or normative influence, has been widely used to explain group polarization. According to the social comparison interpretation, group polarization occurs as a result of individuals' desire to gain acceptance and be perceived in a favorable way by their group. The theory holds that people first compare their own ideas with those held by the rest of the group; they observe and evaluate what the group values and prefers. In order to gain acceptance, people then take a position that is similar to everyone else’s but a little more extreme. In doing so, individuals support the group’s beliefs while still presenting themselves as admirable group "leaders". The presence of a member with an extreme viewpoint or attitude helps to further polarize the group, as the other members will alter their view, making it closer to that persons. Studies regarding the theory have demonstrated that normative influence is more likely with judgmental issues, a group goal of harmony, person-oriented group members, and public responses.
Informational influence, or persuasive arguments theory, has also been used to explain group polarization, and is most recognized by psychologists today. The persuasive arguments interpretation holds that individuals become more convinced of their views when they hear novel arguments in support of their position. The theory posits that each group member enters the discussion aware of a set of items of information or arguments favoring both sides of the issue, but lean toward that side that boasts the greater amount of information. In other words, individuals base their individual choices by weighing remembered pro and con arguments. Some of these items or arguments are shared among the members while some items are unshared, in which all but one member has considered these arguments before. Assuming most or all group members lean in the same direction, during discussion, items of unshared information supporting that direction are expressed, which provides members previously unaware of them more reason to lean in that direction. Group discussion shifts the weight of evidence as each group member expresses their arguments, shedding light onto a number of different positions and ideas. Research has indicated that informational influence is more likely with intellective issues, a group goal of making correct decision, task-oriented group members, and private responses.
In the 1970s, significant arguments occurred over whether persuasive argumentation alone accounted for group polarization. Daniel Isenberg’s 1986 meta-analysis of the data gathered by both the persuasive argument and social comparison camps succeeded, in large part, in answering the questions about predominant mechanisms. Isenberg concluded that there was substantial evidence that both effects were operating simultaneously, and that persuasive arguments theory operated when social comparison did not, and vice-versa.
While these two theories are the most widely accepted as explanations for group polarization, alternative theories have been proposed. The most popular of these theories is self-categorization theory. Self-categorization theory stems from social identity theory, which holds that conformity stems from psychological processes; that is, being a member of a group is defined as the subjective perception of the self as a member of a specific category. Accordingly, proponents of the self-categorization model hold that group polarization occurs because individuals identify with a particular group and conform to a prototypical group position that is more extreme than the group mean. In contrast to social comparison theory and persuasive argumentation theory, the self-categorization model maintains that inter-group categorization processes are the cause of group polarization 
Support for the self-categorization theory, which explains group polarization as conformity to a polarized norm, was found by Hogg, Turner, and Davidson in 1990. In their experiment, participants gave pretest, posttest, and group consensus recommendations on three choice dilemma item-types (risky, neutral, or cautious). The researchers hypothesized that an ingroup confronted by a risky outgroup will polarize toward caution, an ingroup confronted by a caution outgroup will polarize toward risk, and an ingroup in the middle of the social frame of reference, confronted by both risky and cautious outgroups, will not polarize but will converge on its pretest mean. The results of the study supported their hypothesis in that participants converged on a norm polarized toward risk on risky items and toward caution on cautious items. Another similar study found that in-group prototypes become more polarized as the group becomes more extreme in the social context. This further lends support to the self-categorization explanation of group polarization.
Major empirical findings
A number of studies have explored the effects that discussion between groups consisting of like-minded individuals has on members' prevailing opinions.
In 1970, Myers and Bishop selected groups of highly racially prejudiced students and groups of less racially prejudiced students to discuss a number of racial issues. Results demonstrated that racial prejudice decreased for already low-prejudice individuals and increased for already high-prejudice individuals after individuals engaged in their respective group discussion. Thus, their study supported the claim that discussion among like-minded individuals tends to increase and intensify pre-existing attitudes, thereby demonstrating group polarization.
In 2009, an interesting occurrence of group polarization was found in a study conducted by Luhan, Kocher, and Sutter, in which subjects played a ‘dictator game’. In this game, both individual and group decision making was observed to see how individual preferences with respect to the allocation of money between a dictator and a recipient are transformed into a team decision. Their main finding was that team decisions were more selfish and competitive, less trusting and less altruistic than individual decisions. This study therefore offers evidence of group polarization in that the actions of individuals when in a group were more extreme than when the individual acted individually.
Social Comparison Theory
In their 1978 study, Bray and Noble explored the effects of authoritarianism on juror and jury decisions and further investigated the generalizability of the group polarization for a simulated jury task. The underlying assumption of their study was that group interaction tends to enhance choice tendencies initially favored in the subject population. Thus, if predominant sentiment among individual jurors is toward a guilty (not guilty) verdict, that sentiment should be more prevalent following discussion. Their hypothesis regarding group polarization was supported in that they found that deliberations produced a shift toward more severe punishment for high authoritarians but toward more lenient punishment for low authoritarians. Thus, this study provided strong evidence for group polarization in that the groups made decisions that were more extreme than the initial inclination of its members. Mackie (1986) conducted an experiment to explore the Social Comparison Theory. In the experiment, participant’s perceptions and polarization was measured in response to information presented in one of three different conditions: in-group, unrelated group, and uncategorized individual. In accordance with the Social Comparison Theory, researchers expected participants to report greatest polarization in the in-group condition. Polarization should only occur when an individual is exposed to information from their own group. Therefore, researchers expected to see a lower degree of polarization in the unrelated group and uncategorized individual conditions. Mackie (1986) found that attitude polarization occurred only when the participants received information about a group that they considered themselves a member of; supporting the Social Comparison Theory. In their research, Ledgerwood and Chaiken (2007) primed participants with in-group, out-group, or neutral statements. Ledgerwood and Chaiken (2007) used political parties as a way of creating in-groups and out-groups. After being primed, participants were asked to rate how much they agreed with multiple statements that took on either Democratic or Republican views. Researchers hypothesized that participants primed with their political in-group and participants primed with their political out-group would show the highest levels of polarization (strongly agreeing with their in-group and strongly disagreeing with the out-group), compared to the neutral priming condition (or control group). Ledgerwood and Chaiken (2007) found that individuals who identified as Democrats and Republicans, both reported more extreme agreement with their in-group and more extreme disagreement with the out-group, in comparison to the control group, after being primed 
Informational Influence Theory
One of the original studies reporting findings of informational influence was conducted by Stoner (1961). In his study, participants had to advise an imaginary person, who had to make a decision. The imaginary person was choosing from two alternatives. One option was risky but had the potential to have a very positive outcome, where the second option was less risky but had only a moderately positive outcome. Stoner (1961) found that individuals were riskier after discussing the options with the group. A follow-up study was conducted by Myers and Arenson (1972), where they concluded that group discussion does not always result in riskier decision making, however, the individuals original position becomes more extreme after group discussion. After hearing the opinions of others and learning new arguments in favor of their opinion, the individual will become more confident in their decision and their viewpoint becomes more extreme, resulting in group polarization.
In regard to the Informational Influence Theory, Hinsz and Davis (1984) found that it is not simply the sharing of information that is important; however, the amount of information and persuasiveness of the arguments mediate the level of polarization experienced. In their study, Hinsz and Davis( 1984) manipulated the number of arguments and persuasiveness of those arguments. Participants were randomly assigned to a room either by themselves or with 3 other people. Individuals in the alone condition were asked to read through a dilemma and respond. Individuals in the group condition were asked to read through a dilemma and come up with a group consensus. After the individuals and groups were done, they were given a few more minutes to look over the information again, and given the opportunity to change their responses. Researchers came up with a polarization score that was the difference between an individual’s initial response and final response. They found that the higher number of arguments and the higher level of persuasiveness significantly increased polarization. In 1977, Kaplan conducted three experiments in which jurors first heard an incriminating or exonerating trial and then discussed it by exchanging notes with "bogus discussants". The notes differed in the incriminating appearance of shared facts, the redundancy of shared facts, the number of bogus jurors, and the prediscussion judgments of bogus jurors. In instances where the incriminating/exonerating proportion of facts was the opposite of both the trial incriminating/exonerating appearance and the facts cited by the participant, postdiscussion judgment moved away from extremeness. When proportion matched the participant's, judgment became more extreme, yet less so when shared facts were redundant. Kaplan found that neither the number of bogus discussants nor their communicated judgments had an effect. These results did not demonstrate substantial evidence for normative influences, in which judgment shifts in response to normative pressure exerted by knowledge of others' positions. Rather, the result indicate that participants appear to evaluate and integrate information provided by others into their final judgment, in the same manner as they would from any source. This finding provided profound evidence for the informational influence theory explanation.
Group polarization and choice shifts are similar in many ways; however, they differ in one distinct way. The term group polarization is used when discussing the attitude change on the individual level, where the term choice shift is used when discussing the attitude change of a group. Myers and Lam (1976) describe choice shift as the difference between the mean of group members' pre-discussion responses and the actual group decision on an issue.
Risky and cautious shifts are both a part of a more generalized idea known as group-induced attitude polarization. Though group polarization deals mainly with risk-involving decisions and/or opinions, discussion-induced shifts have been shown to occur on several non-risk-involving levels. This suggests that a general phenomenon of choice-shifts exists apart from only risk-related decisions. Stoner  found that a decision is impacted by the values behind that circumstances of the decision. The study found that situations that normally favor the more risky alternative increased risky shifts. More so, situations that normally favor the cautious alternative increased cautious shifts. These findings also show the importance of previous group shifts. Choice shifts are mainly explained by largely differing human values and how highly these values are held by an individual. According to Moscovici et al. interaction within a group and differences of opinion are necessary for group polarization to take place. While an extremist in the group may sway opinion, the shift can only occur with sufficient and proper interaction within the group. In other words, the extremist will have no impact without interaction. Also, Moscovici et al. found individual preferences to be irrelevant; it is differences of opinion which will cause the shift. This finding demonstrates how one opinion in the group will not sway the group; it is the combination of all the individual opinions that will make an impact.
Group processes have also been impacted by the fast-growing popularity of the internet and social media. Studies have found information that both support an increase in group polarization on the internet, while others have found no impact at all. More specifically, with the increasing amount and popularity of online social media such as Facebook and Twitter, it is becoming much easier as well as highly encouraged for people to seek out and share ideas with others who have similar interests and values.
In 2010, Sarita and Boyd analyzed 30,000 tweets on Twitter regarding the shooting of George Tiller, a late term abortion doctor. The tweets analyzed were conversations among pro-life and pro-choice advocates post shooting. They found that like-minded individuals strengthen group identity whereas replies between different-minded individuals reinforce a split in affiliation. This showed that people will group together based on opinions and polarize in one direction no matter what their location is.
In a study conducted by Sia et al. in 2002, group polarization was found to occur with online (computer-mediated) discussions. In particular, this study found that group discussions, conducted when discussants are in a distributed (cannot see one another) or anonymous (cannot identify one another) environment, can lead to even higher levels of group polarization compared to traditional meetings. This is attributed to the greater numbers of novel arguments generated (due to persuasive arguments theory) and higher incidence of one-upmanship behaviors (due to social comparison).
In a study conducted by Taylor & MacDonald in 2002, the results were that even in a realistic setting of a computer-mediated discussion group polarization did not occur at the level expected. The study found that there are differences in laboratory work and field experiments. The researchers suggest that the effects of group polarization lessen when the group is operating in a more natural environment. The experiment took place over a longer amount of time, 2 weeks, and suggests that group polarization may occur only in the short-term. The study's results also showed that group think occurs less in computer-mediated discussions than when people are face to face. More so, computer-mediated discussions often lead to an inability to agree on a consensus and there is usually less satisfaction with the consensus than when groups are operating in a natural environment. Overall, the results suggest that not only may group polarization not be as prevalent as previous studies suggest, but group theories, in general, may not be predictable when seen in a computer-related discussion.
The connection between group polarization and the Internet also has significant applications for friend groups and online bullying. Because it is so easy to communicate with a large number of people, teenagers and young adults can quickly engage in conversation with friends, share opinions, and further strengthen these opinions post sharing them. For example, if a group of girls were discussing how they do not like a certain girl in their class, they could easily and quickly all discuss this online in a chat room. After discussing and sharing their opinions, their opinions would most likely strengthen and intensify. This could then result in the group of girls bullying and harassing the "ostracized" individual. Whether it is online social media or chat rooms, the Internet essentially fosters group polarization for individuals who are using the Internet to communicate. In a day where the Internet and online networking is a huge part of society, group polarization effects are becoming increasingly more evident, particularly in generation Y individuals.
Government, public policy, and the law
||This section may contain original research. (November 2012)|
Group polarization has been widely discussed in terms of political behavior. For example, suppose a group of Republicans sit down to discuss a health care reform and a new policy proposed by a democratic politician. In the beginning of the discussion, the group as a whole may be somewhat against the healthcare reform policy (thus having an initial group attitude). After deliberating the policy, the group may demonstrate that they are now more opposed the policy than ever. In this situation, the initial attitude was reinforced and the group became more polarized against the policy. This type of situation occurs in everyday life as politicians and other people are constantly debating issues surrounding republican versus democrat, abortion versus pro-life, and pro-gay marriage versus anti-gay marriage. In each of these scenarios, there are prominent vocal leaders on each extreme who escalate issues and cause further polarization.
Similar effects of group polarization are evident in the U.S. legal system. In jury deliberations, an essentially random group of people must come to a mutual consensus over whether or not the accused individual is guilty or innocent. Throughout a trial, after discussing with each other, the group may decided on a punishment that was either harsher or more lenient than what any individual juror in the group would have decided individually prior to the group discussion. Group polarization can help explain this decision making process and account for this occurrence.
A real-world example of this was reported by Main and Walker (1973) when they examined the decisions of Federal district court judges sitting either alone or in groups of three to see if group discussions were a factor. In the 1,500 cases where judges sat alone, the judges took an extreme course of action only 30% of the time. However, when sitting in a group of three, the judges took an extreme course of action 65% of the time. These results are noteworthy because they indicate that even trained, professional decision-makers are subject to the influences of group polarization.
War and violent behavior
Group polarization has been reported to occur during war time and other times of conflict. When there is a feud, individuals with the same viewpoint or on the same side, unite and share information; creating a heterogeneous group. During a time of conflict, it is not normal practice for an individual to mingle with the enemy. When individuals with the same views spend all of their time together, their viewpoints become stronger and more extreme. Group polarization can also help in explaining violent behavior. A notable example from history is the Holocaust. During the Holocaust, Hitler united a group of like-minded individuals, Nazis, who shared the common belief that Jews should be exterminated. Once these individuals united into a group, they viewed anyone who didn’t hold Nazi beliefs as outsiders, thus demonstrating polarization. As they polarized, their sense of unity increased and their Nazi pride intensified, ultimately causing them to engage in the violent behavior that they did. Group polarization is also evident in similar situations, such as terrorist attacks and gang violence. While polarization can occur in any type of conflict, it has its most damaging effects in large-scale inter-group, public policy, and international conflicts.
On a smaller scale, group polarization can also be seen in the everyday lives of college students. A study by Myers in 2005 reported that initial differences in college students become more accentuated over time. For example, students who do not belong to fraternities and sororities tend to be more liberal politically, and this difference increases over the course of college at least partially because group members reinforce and polarize each other’s views. Because humans typically associate with people most similar to themselves, interactions tend to strengthen opinions people already have. Therefore, in groups such as fraternities, sororities, and other groups that unify under a label, where ideas and beliefs are likely similar to begin with and further shared, group polarization is extremely commonplace.
In a similar manner, college students are frequently in situations in which they must work in either small or large groups. Whether it be working on a group project for a class or organizing a Greek-life event, students are constantly forced to share their beliefs, ideas, and opinions on whatever the area of concern is. In many of these situations, students may begin with differing or similar opinions; however, as individuals spend more time interacting and discussing with their group, their beliefs are likely to polarize and a resulting group polarization effect may be observed.
While there is ample evidence supporting the phenomenon of group polarization, there is also evidence for the contrary. Many studies have not observed the polarizing effect of groups on decision-making such as Fishkin and Luskin (1999), in which their results indicated that diverse groups do not demonstrate polarization. In a similar manner, not all groups polarize in the same way. Research has suggested that well-established groups suffer less from polarization, as do groups discussing problems that are well known to them. However, in situations where groups are somewhat newly formed and tasks are new, group polarization can demonstrate a more profound influence on the decision-making.
- Adversarial process
- Attitude polarization
- Confirmation bias
- Group-serving bias
- Identity politics
- Aronson, Elliot (2010). Social Psychology. Upper Saddle River, NJ: Prentice Hall. p. 273.
- Myers, D.G.; H. Lamm (1975). "The polarizing effect of group discussion". American Scientist 63 (3): 297–303. Bibcode:1975AmSci..63..297M. PMID 1147368.
- Isenberg, D.J. (1986). "Group Polarization: A Critical Review and Meta-Analysis". Journal of Personality and Social Psychology 50 (6): 1141–1151. PMID 1147368.
- Pruitt, D. (1971). "Choice shifts in group discussion: An introductory review.". Journal of Personality and Social Psychology 20 (3): 339–360. doi:10.1037/h0031922.
- Yardi, Sarita; Danah Boyd (2010). "Dynamic Debates: An analysis of group polarization over time on Twitter". Bulletin of Science, Technology and Society 30 (5): 316–27. doi:10.1177/0270467610380011.
- Stoner, J.A. (1961). "A comparison of individual and group decision involving risk". Unpublished master's thesis, Massachusetts Institute of Technology.
- Forsyth, D.R. (2010) Group Dynamics
- Stoner, James A. F. (1968). "Risky and cautious shifts in group decisions: the influence of widely held values". J. Exp. Social Psychology: 442–459. doi:10.1016/0022-1031(68)90069-3.
- Moscovici, S.; M. Zavalloni (1969). "The group as a polarizer of attitudes". Journal of Personality and Social Psychology 12 (2): 125–135. doi:10.1037/h0027568.
- Van Swol, Lyn M. (2009). "Extreme members and group polarization". Social Influence 4 (3): 185–199. doi:10.1080/15534510802584368.
- Vinokur, A.; Burnstein, E. (1974). "Effects of partially shared persuasive arguments on group induced shifts: A group problem-solving approach". Journal of Personality and Social Psychology: 305–315.
- Abrams, D.; M. Wetherell, S. Cochrane, M.A. Hogg, & J.C. Turner (1990). "Knowing what to think by knowing who you are: Self-categorization and the nature of norm formation, conformity and group polarization". British Journal of Social Psychology 29 (2): 97–119. doi:10.1111/j.2044-8309.1990.tb00892.x. PMID 2372667.
- Hogg, M.A.; Turner, J.C. & Davidson, B. (1990). "Polarized norms and social frames of reference: A test of the self-categorization theory of group polarization". Basic and Applied Social Psychology: 77–100. doi:10.1207/s15324834basp1101_6.
- McGarty, Craig; John C. Turner, Michael A., Barbara David, et al (March 1992). "Group polarization as conformity to the prototypical group member". British Journal of Social Psychology 31: 1–19. doi:10.1111/j.2044-8309.1992.tb00952.x.
- Myers, David G.; G.D. Bishop (1970). "Discussion effects on racial attitude". Science 169 (3947): 778–779. Bibcode:1970Sci...169..778M. doi:10.1126/science.169.3947.778.
- Luhan, Wolfgang J.; Martin G. Kocher & Matthias Sutter (2009). "Group Polarization in the Team Dictator Game Reconsidered". Experimental Economics 12 (1): 26–41. doi:10.1007/s10683-007-9188-7.
- Ledgerwood, Alison coauthors=Shelly Chaiken (2007). "Priming Us and Them: Automatic Assimilation and Contrast in Group Attitudes". Journal of Personality and Social Psychology 93 (6): 940–956. doi:10.1037/0022-3518.104.22.1680. PMID 18072847.
- Myers, D.G. coauthors=S.J. Arenson (1972). "Enhancement of dominant risk tendencies in group discussion". Psychological Reports: 615–623. doi:10.2466/pr0.1922.214.171.1245.
- Hinsz, V.B. coauthors=J.H. Davis (1984). "Persuasive Arguments Theory, Group Polarization, and Choice Shifts". Personality and Social Psychology Bulletin: 260–268. doi:10.1177/0146167284102012.
- Kaplan, Martin F. (September 1977). "Discussion Polarization Effects in a Modified Jury Decision Paradigm: Informational Influences". Sociometry. 3 40 (3): 262–271. doi:10.2307/3033533.
- Myers, D.G.; H. Lamm (1976). "The group polarization phenomenon". Psychological Bulletin: 602–627. doi:10.1037/0033-2909.83.4.602.
- Moscovici, S.; W. Doise, R. Dulong (1972). "Studies in group decision: II. Differences of positions, differences of opinion, and group polarization". European Journal: 385–399. doi:10.1002/ejsp.2420020404.
- Sia, C. L; Tan, B & Wei, K. K. (2002). "Group Polarization and Computer-Mediated Communication: Effects of Communication Cues, Social Presence, and Anonymity". Information Systems Research 13: 70–90. doi:10.1287/isre.126.96.36.199.
- Taylor, J. coauthors=J. MacDonald (2002). "The effects of asynchronous computer-mediated group interaction of group processes". Social Science Review: 260–274. doi:10.1177/089443930202000304.
- Feilitzen, C. (2009). Influences of mediated violence: a brief research summary. International clearninghouse on children, youth and media. ISBN 978-91-89471-81-8.
- Walker, Thomas G.; Main, Eleanor C. (December 1973). "Choice shifts and extreme behavior: Judicial review in the federal courts". The Journal of Social Psychology. 2 91 (2): 215–221. doi:10.1080/00224545.1973.9923044.
- Sunstein, C.R. (2002). "The Law of Group Polarization". The Journal of Political Philosophy 10 (2): 175–195. doi:10.1111/1467-9760.00148.
- Newman, L.S. (2002). Understanding Genocide: The Social Psychology of the Holocaust. New York, NY: Oxford University Press. pp. 143–161. ISBN 0-19-513362-5.
- Griggs, Richard (2009). Psychology: A concise introduction. New York: Worth Publishers. p. 306.