"Group behavior" refers to the ways people behave in large- or small-group situations. People join groups for a multitude of reasons, most frequently because membership satisfies a need of the individual. Group membership can provide companionship, survival and security, affiliation status, power and control, and achievement. There is currently no universal description of what constitutes a group, though research has identified a few common requirements that contribute to recognition of a group:

• Interdependence—Individual members must depend, to some degree, on the output of the collective members.
• Social interaction—Accomplishing a goal requires some form of verbal or nonverbal communication among members.
• Perception of a group—All members of the collective must agree they are part of the group.
• Commonality of purpose—All members of the collective come together to attain a common goal.
• Favoritism—Members of the same group tend to be positively prejudiced toward other members and discriminate in their favor.

How Groups Influence Individual Behavior

Individual behavior and decision making can be influenced by the presence of others. There are both positive and negative implications of group influence on individual behavior. For example, group influence can often be useful in the context of work settings, team sports, and political activism. However, the influence of groups on the individual can also generate negative behaviors.

While there are many ways a group can influence behavior, we will focus on three key phenomena: groupthink, groupshift, and deindividuation. Groupthink happens when group members, faced with an important choice, become so focused on making a smooth, quick decision that they overlook other, possibly more fruitful options. Groupshift is a phenomenon in which the initial positions of individual members of a group are exaggerated toward a more extreme position. Deindividuation happens when a person lets go of self-consciousness and control and does what the group is doing, usually with negative goals or outcomes. We will discuss these more in detail below. 

Groupthink

Groupthink is a psychological phenomenon that occurs within a group of people, in which the desire for harmony or conformity in the group results in an incorrect or deviant decision-making outcome. It has been further defined as a mode of thinking that people engage in when they are deeply involved in a cohesive group, when the members' strivings for unanimity override their motivation to realistically appraise alternative courses of action.

Group members try to minimize conflict and reach a consensus decision without critical evaluation of alternative ideas or viewpoints. Several conditions must take place for groupthink to occur: the group must be isolated from outside influences;  loyalty must prevent individuals from raising controversial issues of alternative solutions; there must be a loss of individual creativity and independent thinking; and the group must experience the "illusion of invulnerability," an inflated certainty that the right decision has been made. Typically the group is under a high level of pressure to make a decision, and it lacks an impartial leader. These factors can lead a group to make a catastrophically bad decision. Nazi Germany is often cited as a prime example of the negative potential of groupthink because a number of factors, such as shared illusions and rationalizations and a lack of individual accountability, allowed for a few powerful leaders to enlist many otherwise "normal" people in committing mass acts of violence.

While groupthink is generally accepted as a negative phenomenon, it has been proposed that groups with a strong ability to work together are able to solve problems more efficiently than individuals or less cohesive groups.

Groupthink

This image outlines the requirements, symptoms, and defects of groupthink in detail. Groups must be cohesive, insulated, lack an impartial leader, and homogenous, as well as be in a provocative, high stress situation, in order for groupthink to occur.

Groupshift

Groupshift is the phenomenon in which the initial positions of individual members of a group are exaggerated toward a more extreme position. When people are in groups, they assess risk differently than they do when they are alone. In the group, they are likely to make riskier decisions as the shared risk makes the individual risk seem to be less.

What appears to happen in groups is that discussion leads to a significant shift in the position of the members to a more extreme position in the direction they were all already leaning. A group of moderate liberals may shift from moderate to strongly liberal views when in a group together. A group of mildly racist people may become viciously racist when together. The theory behind this shift is that the group dynamic allows the individual members to feel that their position is correct or supported, and they will feel more comfortable taking on more extreme views, as other members of the group support their initial ideas. The extreme ideas seem less risky as it appears the view is held by numerous like-minded people.

Deindividuation

Deindividuation is exactly what the word implies: a loss of one's individuality. Instead of acting as individuals, people experiencing deindividuation become lost in a group. This often means that they will go along with whatever the group is doing, whether it be rioting, looting, lynching, or engaging in cyberbullying. Some people posit that this happens because individuals experience a sense of anonymity in a group. The larger the group, the higher the incidence of deindividuation, which is characterized by an individual relinquishing self-consciousness and control and doing what the group is doing. This occurs when people are moved by the group experience to do things that, without the group for support, they would not normally do. 

It is important to distinguish deindividuation from obedience (when a person yields to explicit instructions or orders from an authority figure), compliance (when a person responds favorably to a request from others) and conformity (when a person attempts to match his attitudes to group norms, versus the total relinquishing of individuality seen in deindividuation).