Leadership is more than managing tasks and overseeing operations; it’s about understanding the complex web of human interactions that drive team performance. At the heart of this understanding lies group dynamics and team psychology—fields that explore how individuals behave in collective environments and how their behavior shifts based on group structure, roles, and interdependence. Whether you’re leading a small project team or managing a multinational organization, leveraging insights from psychology can significantly improve how your teams function.

Over the past century, researchers have conducted numerous experiments to understand how groups form, operate, and achieve—or fail to achieve—success. These experiments provide crucial insights into how teams can be more than just the sum of their parts, offering practical strategies that leaders can apply to enhance collaboration, decision-making, and overall productivity.

However, the power of these studies goes beyond mere theory. Many leaders make the mistake of believing that successful teams form naturally, driven by shared goals and a common purpose. But the reality is far more nuanced. Groups are often fraught with pitfalls: miscommunication, conflict, social loafing, and groupthink can derail even the most well-intentioned team. Effective leadership requires a deep understanding of the psychological forces that influence team behavior, whether you’re dealing with the social facilitation effect, the risk of conformity, or the motivational dynamics within diverse teams.

1. Google’s Project Aristotle (2012-2015)

Study: Google's People Operations team embarked on an ambitious project to understand what made some teams perform better than others. Analysing over 180 teams over two years, they discovered that psychological safety—the belief that team members won’t be punished for making mistakes—was the most crucial element in high-performing teams. Other factors, such as dependability, structure, meaning, and impact, also played important roles, but psychological safety remained the key differentiator.

Methodology: Over 200 interviews were conducted with employees, and hundreds of data points—ranging from employee personality traits to team size—were analysed. Google used this data to map how these variables correlated with team effectiveness and performance.

Findings: The research revealed that psychological safety allowed teams to be more open to sharing ideas, admit mistakes, and take risks, leading to higher innovation and productivity. Teams that felt safe were more likely to engage in constructive conflict, collaborate effectively, and problem-solve as a unit.

Key Takeaway for Leaders: To foster an environment that promotes high performance, prioritise creating psychological safety. Encourage open communication, risk-taking, and create space for learning from mistakes.

2. Dunbar’s Number (2010)

Study: Robin Dunbar’s work proposes that humans can maintain stable relationships with only a finite number of people—around 150—due to cognitive limits. This threshold is now referred to as “Dunbar’s Number.” Beyond this number, relationships become less personal and meaningful.

Methodology: Dunbar’s research was based on an analysis of primate social groups and a comparative study of neocortex size (the part of the brain responsible for higher cognitive functions). He expanded this research to human communities, studying social groupings in villages, businesses, and even online social networks.

Findings: Dunbar found that as social groups increase in size beyond approximately 150 members, interpersonal connections deteriorate, resulting in weaker relationships and more superficial interactions.

Key Takeaway for Leaders: To maintain cohesion and communication, keep teams and departments small enough that individuals can form meaningful relationships. Larger groups risk disconnection, which can lead to miscommunication and reduced collaboration. When considering your extended networks overlay Dunbars number in your thought processes.

3. The Kohler Effect (1926, Reanalysis in 2009)

Study: Otto Köhler’s original research in 1926 demonstrated that weaker team members tend to exert more effort when working alongside stronger team members in order to avoid being the weakest link. This effect, known as the Kohler Effect, was later reanalysed in 2009 in the context of workplace teams.

Methodology: Köhler’s experiment involved studying rowers in a gymnasium setting. He measured individual performance when rowing alone versus in a group. The 2009 reanalysis applied this concept to business environments, assessing how performance improved when less skilled employees worked alongside higher performers.

Findings: Weaker team members worked harder when paired with stronger individuals, especially in tasks that were essential to the team’s success. In modern work settings, this dynamic continues to hold, where individuals raise their performance in group situations to avoid being the limiting factor.

Key Takeaway for Leaders: Pair individuals with different skill levels to encourage growth and motivation. Perceived weaker performers will push themselves harder when they see stronger teammates excelling, leading to better overall team performance.

4. Group Polarization (1970s, Reanalyzed in the 2000s)

Study: Serge Moscovici and colleagues studied how group discussions lead to more extreme decisions than individuals would make alone. This phenomenon, known as group polarization, was originally observed in the 1970s and reanalyzed in the 2000s to understand how it manifests in modern organizations.

Methodology: Group discussions were facilitated where individuals expressed their initial opinions. After a period of group discussion, researchers measured how much the opinions shifted. They found that group discussions led to more extreme versions of the individuals’ pre-existing attitudes.

Findings: Group polarization occurs most strongly in homogenous groups—when members share similar views, discussions tend to amplify the extremity of those views. This can lead to riskier or more conservative decisions, depending on the group’s starting point.

Key Takeaway for Leaders: To prevent extreme decision-making, encourage diverse perspectives within teams. Fostering a mix of opinions can help balance group discussions and lead to more measured, thoughtful decisions.

5. Belbin’s Team Roles (1981)

Study: Meredith Belbin’s nine-year study identified nine distinct team roles that individuals naturally adopt. These roles, such as the Coordinator, Shaper, and Implementer, are essential for building a balanced and high-performing team.

Methodology: Belbin observed teams working on complex projects, noting how individuals contributed and interacted. Over time, patterns emerged, revealing that teams where different roles were present tended to perform better than teams where everyone shared similar strengths.

Findings: Successful teams consist of a mix of roles, each contributing uniquely to the team’s overall function. Diversity in roles fosters stronger collaboration and ensures that a team’s weaknesses are mitigated by complementary strengths.

Key Takeaway for Leaders: Assess your team members to identify their natural roles and ensure that all nine roles are represented in your team. Balancing these roles creates a stronger, more cohesive team dynamic.

6. The Jigsaw Classroom (1971, Corporate Applications in the 2000s)

Study: Elliot Aronson developed the Jigsaw Classroom to reduce racial conflict in schools by assigning students interdependent roles in group tasks. In the 2000s, this model was successfully adapted to corporate environments to foster collaboration.

Methodology: In the Jigsaw method, each team member is given a critical piece of information that the rest of the group needs in order to complete the task. This interdependence forces cooperation, communication, and engagement from all team members.

Findings: Groups that required interdependent work performed better and reported higher satisfaction. By making each member’s contribution indispensable, the method also increased accountability and motivation.

Key Takeaway for Leaders: Structure tasks so that each team member’s contribution is essential to the group’s success. This method increases engagement, fosters collaboration, and boosts morale.

7. The Broken Windows Theory (1982, Organizational Applications in 2004)

Study: James Q. Wilson and George Kelling’s Broken Windows Theory argues that visible signs of disorder, like broken windows or graffiti, lead to further crime and disorder. This theory was later applied to workplace culture to understand how minor infractions or neglect could snowball into more serious issues.

Methodology: Researchers observed the impact of small environmental cues, such as untidiness or minor rule-breaking, in communities and workplaces. They found that environments with unaddressed disorder tended to experience more serious problems, such as absenteeism or low morale, over time.

Findings: Minor issues, when left unaddressed, signal to employees that standards are not being upheld, leading to more significant problems. Maintaining a well-ordered environment fosters better behavior and discipline.

Key Takeaway for Leaders: Address small problems as they arise, whether behavioural or environmental. Creating a respectful, orderly workspace leads to greater accountability and productivity.

8. Transactional vs. Transformational Leadership (1978, Ongoing Studies)

Study: James Burns introduced the distinction between transactional and transformational leadership styles. Transactional leaders focus on exchanges—offering rewards for performance—while transformational leaders inspire and motivate their teams toward greater goals.

Methodology: Burns conducted in-depth interviews with political and business leaders to understand the relationship between leadership style and effectiveness. His research expanded into the corporate world, where he compared the short-term, task-focused success of transactional leaders with the long-term, visionary success of transformational leaders.

Findings: Transformational leaders, who inspire their teams with a compelling vision, were found to foster greater loyalty, motivation, and innovation. While transactional leadership works well for short-term, goal-specific tasks, it is less effective in driving long-term engagement and growth.

Key Takeaway for Leaders: Focus on being a transformational leader by inspiring your team with a long-term vision. Motivate them to surpass personal and organizational goals through empowerment and purpose.

9. The Ringelmann Effect (1913)

Study: Max Ringelmann’s 1913 study found that individuals tend to put in less effort as group size increases—a phenomenon known as social loafing.

Methodology: In Ringelmann’s original experiment, participants were asked to pull on a rope, either alone or in a group. He found that as more people joined the task, individual effort decreased.

Findings: In larger teams, individuals may assume that others will pick up the slack, leading to reduced overall effort. Social loafing is more pronounced in tasks where individual contributions are not clearly identifiable.

Key Takeaway for Leaders: To prevent social loafing, keep teams small and assign clear responsibilities to each member. Ensuring that each person’s contribution is visible helps maintain accountability and effort.

10. Asch Conformity Experiments (1951, Revisited in the 2000s)

Study: Solomon Asch’s classic conformity experiments demonstrated how group pressure can lead individuals to conform, even when they know the group’s opinion is wrong. This has significant implications for decision-making in teams.

Methodology: Participants were asked to match line lengths on cards, with the correct answer being obvious. However, participants were placed in groups, with confederates instructed to provide incorrect answers intentionally. Despite the clear evidence that the confederates' answers were wrong, a significant number of participants conformed to the group’s incorrect choice rather than trusting their own judgment.

Findings: The experiments demonstrated that group pressure can significantly alter individual decision-making. Even when participants knew the correct answer, many still conformed to the group’s erroneous consensus, highlighting the power of social influence.

Revisited in the 2000s: Modern versions of Asch’s experiment explored how conformity works in digital settings and virtual teams. These studies showed that online group pressure can similarly lead to conformity, especially in environments where dissenting opinions are downvoted or ignored in favor of majority views.

Key Takeaway for Leaders: Foster a culture of independent thinking and ensure that diverse opinions are valued. Create an environment where employees feel comfortable challenging the status quo and sharing alternative perspectives without fear of being ostracized.

11. The Pygmalion Effect (1968)

Study: The Pygmalion Effect, or the power of expectations, was explored by Robert Rosenthal and Lenore Jacobson in a study that found higher expectations from teachers resulted in better academic performance by students. This psychological phenomenon has since been applied to leadership in organisational contexts, where leaders’ expectations of their teams can profoundly affect performance.

Methodology: In the original study, teachers were informed that certain students (randomly selected) were expected to show significant intellectual growth during the school year. Despite no differences in ability, these students performed better than their peers by the end of the year, largely due to the teachers’ belief in their potential.

Findings: Leaders’ attitudes and expectations about their employees’ abilities can shape performance. Positive expectations often lead to higher motivation, greater effort, and improved outcomes, while negative expectations can have the opposite effect.

Key Takeaway for Leaders: Set high but realistic expectations for your team. Believe in their potential to succeed, and they are more likely to meet or even exceed those expectations. This helps create a positive feedback loop where employees feel motivated to achieve more.

12. The Social Facilitation Effect (1898)

Study: Norman Triplett, often credited with conducting the first formal social psychology experiment in 1898, observed that cyclists performed better when racing against others than when racing against the clock. To further investigate this, Triplett conducted an experiment with children winding a reel, finding that they completed the task faster when in the presence of others. This phenomenon was termed "social facilitation" and refers to how people perform better on simple or well-learned tasks when others are present but struggle with complex tasks under the same conditions.

Method: In his experiment, Triplett had children wind fishing reels either alone or in pairs, measuring the time taken to complete the task. Results showed faster completion times when the children worked in pairs. This observation led to further research into how the presence of others affects performance, with later studies confirming that while performance improves on simple tasks, it often declines on more complex tasks due to increased pressure.

Reanalysis in the 2000s: Researchers in the 21st century expanded on this concept, studying the effect in modern workplaces. They found that in routine or repetitive tasks, such as data entry or assembly line work, performance could be enhanced in a team setting. However, in creative, problem-solving, or strategic tasks, individuals tend to perform better alone, free from the pressure of observation.

Key Takeaway for Leaders: Use team settings for routine, repetitive tasks to boost performance, but allow individuals to work alone on some complex or creative tasks. This will prevent performance anxiety and foster better problem-solving.

13. Tuckman’s Stages of Group Development (1965, Refined in the 2000s)

Study: Bruce Tuckman developed a model of group development in 1965, identifying four key stages that teams pass through: Forming, Storming, Norming, and Performing. In the Forming stage, team members get to know one another and begin to define roles. Storming is marked by conflict and power struggles as individuals vie for influence. As teams move into the Norming stage, roles and processes are established, and the team starts working more cohesively. Finally, in the Performing stage, the team operates efficiently towards shared goals.

Method: Tuckman’s model was based on a review of 50 different studies on group development. He later added a fifth stage, Adjourning (sometimes called "Mourning"), which represents the dissolution of the group after task completion.

Reanalysis in the 2000s: Subsequent research validated Tuckman’s model in various industries, confirming that teams pass through these stages, albeit at different paces. The model was refined to reflect that teams can regress to earlier stages when faced with new challenges or changes, like leadership shifts or new team members.

Key Takeaway for Leaders: Guide your teams through each developmental stage and recognize that conflict during the Storming stage is natural. Support your team by providing clear direction during conflict and by reinforcing positive collaboration during the Norming and Performing stages.

14. Deindividuation (1952)

Study: Leon Festinger and his colleagues introduced the concept of deindividuation in 1952 to explain how individuals in large groups may lose their sense of self-awareness and responsibility, leading them to act in ways they wouldn’t typically consider. This phenomenon is often linked to mob behavior, where the anonymity of a crowd can lead to impulsive or unethical actions.

Method: Festinger’s studies involved participants in various group sizes and anonymity levels, examining their behaviors in tasks requiring judgment and ethical decision-making. He found that as group size increased or anonymity was provided, individuals were more likely to engage in behaviours they would usually avoid, such as lying or aggression.

Reapplication in the 2000s: In corporate settings, researchers reexamined deindividuation to understand how anonymity in large organizations or virtual teams can lead to unethical behavior, reduced accountability, and lower productivity. This research revealed that individuals in large teams or those working remotely without personal accountability could disengage from their responsibilities.

Key Takeaway for Leaders: To counteract deindividuation, ensure that individuals in large teams or virtual settings maintain personal responsibility for their actions. Assign clear, individual tasks and hold regular check-ins to keep team members accountable.

15. Groupthink (1982)

Study: Irving Janis coined the term "groupthink" to describe how the desire for harmony and consensus in a group can lead to irrational decision-making (groupthink was alos attributed as a root cause of the Challenger Space Shuttle disaster). Groupthink occurs when members suppress dissenting opinions, often because they don’t want to disrupt the group’s cohesion or because they assume their concerns are already considered by the majority. After all, moving in time with others is a central characteristic of social life and has been shown to promote a host of social-cognitive attunements (e.g., person memory, affiliation, prosociality) for those involved.

Method: Janis analyzed several historical case studies, including the Bay of Pigs invasion and the escalation of the Vietnam War, where poor decisions were made due to the lack of critical analysis. He identified several symptoms of groupthink, including the illusion of invulnerability, rationalisation, and self-censorship.

Ongoing Studies: Recent research continues to explore groupthink in modern organizations. Studies have shown that homogeneous teams, especially those led by authoritarian leaders, are more susceptible to groupthink, leading to missed opportunities and increased risk.

Key Takeaway for Leaders: Encourage open dialogue and debate within your team to avoid the pitfalls of groupthink. Promote a culture that values diverse perspectives and critical thinking, ensuring that dissenting voices are heard and considered.

16. The Bystander Effect (1968, Reanalyzed in 2000s)

Study: John Darley and Bibb Latané’s experiments were sparked by the infamous case of Kitty Genovese, where a young woman was murdered in New York City while dozens of neighbours reportedly failed to intervene. The researchers found that individuals are less likely to take action in an emergency when they believe others will, a phenomenon known as the bystander effect.

Method: In controlled laboratory experiments, participants were placed in situations where they believed others were witnessing an emergency. The more people present, the less likely any individual was to act.

Reanalysis in the 2000s: This concept was applied to organisational settings, where shared responsibilities without clear accountability led to inaction or neglect of duties. Studies confirmed that in large teams, individuals often assume someone else will handle a task, leading to delays or mistakes.

Key Takeaway for Leaders: Clearly define individual responsibilities within teams. Avoid assigning tasks to large groups without specifying who is accountable for each element, ensuring that every team member knows their role.

17. The Robbers Cave Experiment (1954, Revisited in 2000s)

Study: Muzafer Sherif’s famous field experiment at Robbers Cave State Park demonstrated how intergroup conflict arises from competition and how cooperation can dissolve these tensions. In the study, two groups of boys at a summer camp were initially set against each other in competitive activities, leading to hostility and conflict. Later, they were given tasks that required cooperation, such as fixing a water supply, which reduced tension and promoted unity.

Method: Sherif’s experiment involved realistic group conflict theory, where groups were placed in situations where resources were limited, creating competition. Over time, the experiment showed that shared goals could bring the groups together. A useful finding for team and organisational life.

Revisited in 2000s: This experiment was revisited in corporate settings, where researchers explored how competition between teams can breed division and conflict. Cooperative goals, such as company-wide initiatives, were found to promote unity and reduce interdepartmental rivalry.

Key Takeaway for Leaders: Foster collaboration between teams by creating shared goals that require cooperation. This reduces internal competition and builds a sense of unity and common purpose across the organization.

18. Milgram’s Obedience Experiment (1961)

Study: Stanley Milgram’s experiment demonstrated the extent to which people would obey authority figures, even when instructed to perform actions they believed were morally wrong. In the study, participants were told to administer increasingly painful electric shocks to another person (an actor) at the instruction of an experimenter. Many participants continued administering shocks, despite hearing the actor’s screams, simply because they were told to do so by an authority figure.

Method: Participants were placed in a controlled environment where they believed they were administering real shocks to a person in another room. The study measured how far individuals would go under the influence of an authoritative figure. Modern research has examined the implications of authority in workplace settings, especially in hierarchical organisations. Studies show that employees may follow unethical directives when issued by a higher authority, even if they conflict with personal values.

Key Takeaway for Leaders: Exercise authority ethically and responsibly. Ensure that your team members feel empowered to question directives that may seem unethical or misaligned with company values and of course consider ethics/whistleblower helplines.

19. The Hawthorne Effect (1924-1932)

Study: The Hawthorne Effect refers to a phenomenon where individuals modify their behavior in response to being observed. This was first identified during a series of experiments at Western Electric’s Hawthorne Works in Chicago from 1924 to 1932 (though the term was coined by John French in 1953). The goal of the original study was to determine whether improving lighting would increase worker productivity. Surprisingly, regardless of whether lighting was improved or dimmed, productivity increased simply because the workers believed they were being watched.

Methodology: The original study consisted of multiple phases. In one phase, researchers altered the lighting in the workspaces of a group of workers, and then measured changes in productivity. In subsequent phases, they altered other working conditions such as break times, work hours, and wages to see if these changes had any effect. The consistent result was that productivity increased, even when the changes were reversed or made worse.

Reanalysis in the 2000s: The Hawthorne Effect has since been revisited in modern organisational psychology, particularly in relation to employee performance monitoring. Studies in the 2000s expanded on the idea, showing that even today, employees tend to work more efficiently when they know they’re being observed, whether by supervisors or through performance tracking systems.

Findings: The study concluded that it wasn’t the environmental changes that drove increased productivity, but rather the workers’ awareness of being monitored. When employees feel their efforts are being seen and valued, they are more likely to engage and perform at a higher level.

Key Takeaway for Leaders: Provide regular feedback and recognition to your team. Ensure employees know their efforts are noticed and appreciated. This boosts engagement and productivity, as people are more likely to invest effort when they feel they’re being valued.

20. Social Identity Theory (1979)

Study: Henri Tajfel’s Social Identity Theory explores how individuals derive a sense of identity from the groups they belong to. Tajfel’s research was originally conducted to understand the psychological basis for intergroup discrimination, such as racial or cultural biases. The theory explains how in-group favoritism and out-group discrimination can develop as a result of individuals identifying strongly with one group (the in-group) while categorizing others as part of an out-group.

Methodology: Tajfel conducted experiments with minimal group paradigms, where participants were arbitrarily assigned to groups based on meaningless criteria (e.g., preferences for certain paintings). Despite the random assignment and lack of meaningful group differences, participants showed favoritism towards their own group and were more willing to allocate resources to in-group members at the expense of the out-group. Researchers revisited Social Identity Theory in the context of corporate environments, particularly in large organizations where departments or teams often develop strong group identities. Studies found that strong in-group identification could lead to competitive behavior between departments, reducing overall organizational unity and increasing interdepartmental conflict.

Findings: Tajfel’s work showed that people are prone to favor their own group, often without rational justification. In modern workplace settings, this can manifest as siloed departments competing for resources or recognition, which can harm overall collaboration and organizational performance.

Key Takeaway for Leaders: While fostering a strong team identity is important, leaders must be mindful of preventing divisions between teams, departments, or other groups within the organization. Encourage a culture of inclusivity, where collaboration and cross-team interaction are prioritized. Reducing the "us vs. them" mentality can help diminish in-group favouritism and promote a more harmonious work environment.

Conclusion

This article outlines key group psychology experiments that provide valuable insights for leaders aiming to optimize team performance. Key studies such as Google’s Project Aristotle emphasize the importance of psychological safety in fostering high-performing teams, while Dunbar’s Number highlights the cognitive limits of maintaining meaningful relationships, advising leaders to keep team sizes manageable.

The Kohler Effect suggests that weaker team members improve their performance when paired with stronger ones, and Group Polarization warns against homogeneous teams making extreme decisions. Belbin’s Team Roles and The Jigsaw Classroom underscore the need for diverse roles and interdependence within teams to enhance collaboration and accountability.

Leadership styles are explored through Transactional vs. Transformational Leadership, with the latter being more effective for long-term engagement. Additionally, studies like The Ringelmann Effect (social loafing) and Asch’s Conformity Experiments (group pressure) reveal common pitfalls in teamwork that leaders must mitigate by fostering accountability and independent thinking.

Finally, Social Identity Theory and The Pygmalion Effect highlight the significance of fostering inclusivity and setting high expectations to motivate teams while avoiding in-group favoritism. By applying these psychological insights, leaders can improve team cohesion, innovation, and overall productivity.