Interdependence theory is a type of social exchange theory used in social psychology. It studies how people in relationships affect each other's experiences. This theory was first introduced by Harold H. Kelley and John Thibaut in 1959. It helps explain how people's actions in relationships are influenced by both their own choices and the choices of others.

A key idea in the theory is shown by the equation I = ƒ[A, B, S]. This means that all interactions between people depend on the situation (S) and the actions and traits of the people involved (A and B). This equation shows how people's actions, thoughts, and feelings in relationships are shaped by both the situation and their personal mental processes.

The theory's four basic assumptions are:

Authors

Interdependence theory was first introduced by Harold Kelley and John Thibaut in 1959 in their book The Social Psychology of Groups. This book was influenced by ideas from social exchange theory and game theory, and it explained important definitions and concepts that helped shape the interdependence framework. In 1978, they published another book titled Interpersonal Relations: A Theory of Interdependence, where they made the theory more detailed. In 2003, Harold Kelley expanded the theory further in his book An Atlas of Interpersonal Situations. This book added two new dimensions to the theory and described 21 different types of situations. The work of Kelley and Thibaut was also based on the earlier ideas of Kurt Lewin, who first described interdependence. Lewin stated, "The main idea of a group is not how similar or different its members are, but how they depend on each other. A change in one part of the group affects all other parts. When one member moves, it deeply influences the others, and the whole group changes."

Four basic assumptions of interdependence theory

All interactions happen in a specific situation (called "structure" in Interdependence theory). To understand this, Interdependence theory uses a system to describe different types of situations. A key idea in this system is "affordance," which means what the situation allows individuals to do during the interaction.

Six dimensions of structure:

• Degree/level of dependence. This describes how much one person in an interaction relies on another person. It includes three types of control:
• Actor Control: When a person’s actions directly affect their own results.
• Partner Control: When a person’s actions affect the results of others.
• Joint Control: When both people’s actions together affect each other’s results.
• For example, if Person A can achieve a good result no matter what Person B does, Person A has high Actor Control. If Person A needs Person B’s actions to get a good result, Person A has high Partner Control. If both people need each other to get good results, they have high Joint Control.

• Mutuality of dependence. This looks at how equally each person depends on the other. If Person A depends more on Person B, Person B has more control over Person A.

• Covariation of interest. This describes how much each person benefits from the results of the interaction. It can range from both people benefiting equally (coordination) to one person’s benefit being the other’s loss (zero-sum). For example, if both people achieve their goals by working together, that’s coordination. If one person’s gain causes the other’s loss, that’s conflicting.

• Basis of dependence. This refers to how one person influences another. It includes the same three types of control as above: Actor Control, Partner Control, and Joint Control. Examples of how influence happens include promises, threats, following rules, acting alone, or taking turns.

• Temporal structure. This focuses on how timing and the order of events affect situations. Key ideas include:
• Situational Selection: Moving from one situation to another, where new choices or results are available.
• The shadow of the future: Planning to cooperate now in hopes of future rewards from the other person.

• Information availability. This refers to how much each person knows about the other’s goals, possible results, and future chances. If one person has more information, they may act differently than if they had less.

Transformation is a process where people think about the results of their actions and the actions of others. They compare these results to the choices they can make (called "rewards" and "costs").

• Rewards and costs. Interdependence theory says the best relationships have high rewards and low costs.
• Rewards are things that make people happy, like kindness or help.
• Costs are things that cause loss or problems, like arguments or effort.
• There are four types of rewards and costs:
• Emotional: Feelings of happiness or sadness in a relationship.
• Social: How people are seen in social groups or how enjoyable social situations are.
• Instrumental: Help with tasks, like someone doing chores.
• Opportunity: Gains or losses from chances that come from being in a relationship.

Outcome transformation is when people consider both their own results and the other person’s results in an interaction. Some ways people think about others’ results include:
– Cooperation (MaxJoint): Focusing on achieving the best results for both people.
– Equality (MinDiff): Making sure both people get similar results.
– Altruism (MaxOther): Focusing on helping the other person.
– Aggression (MinOther): Focusing on harming the other person.

The Principle of Interaction (also called the SABI model) helps explain what affects an interaction. It says that an interaction (I) depends on the situation (S), Person A’s motives, traits, and actions (A), and Person B’s motives, traits, and actions (B). The formula is:
I = ƒ[A, B, S]

Factors that affect interactions include:
– Outcomes: The results of a relationship, based on how much people gain (rewards) versus how much they lose (costs).
– Comparison Level: How people judge their relationship based on what they expect.
– Comparison Level for Alternatives: How people judge their relationship compared to other possible relationships.

"According to interdependence theory, people mentally compare the rewards and costs in their relationships to understand their experiences."

Academic and practical applications

Interdependence theory has been used by scholars to study group behavior, power and reliance, social comparisons, conflict and teamwork, how people explain others' actions and present themselves, trust and distrust, emotions, love and commitment, coordination and communication, risk and self-control, performance and motivation, social growth, and models of how the brain affects social interactions (Van Lange & Balliet, 2014, p. 67).

This theory also offers a useful way to understand the reasons behind how other people act in both personal and professional situations. It also helps explain the reasons behind how you act when interacting with others.

Complementary/related theories and frameworks

• Goal-Expectation Theory: How people set goals and what they expect from them.
• Structural Goal-Expectation Theory: How goals and expectations are organized in groups or systems.
• The Individual–Group Discontinuity Model: How people change when they move from being part of a group to being an individual.
• Game Theory: How people make decisions when they are competing or working together, like in games.
• Theories of Direct Reciprocity and Indirect Reciprocity: Direct Reciprocity: helping others who have helped you before. Indirect Reciprocity: helping others because others might help you in the future.
• Need-to-Belong Model: How people need to feel connected to others and what happens when they don’t.
• The Investment Model of Commitment Processes: How people stay committed to relationships by investing time, effort, or resources.
• The Model of Communal (and Exchange) Orientations (in Close Relationships): How people share resources or help each other in close relationships, either equally or based on needs.
• The Empathy–Altruism Model (Explaining Altruism and Prosocial Behavior): How feeling empathy leads people to help others without expecting anything in return.
• Realistic Conflict Theory (Applied to Intergroup Processes): How real conflicts between groups can lead to dislike or competition between them.
• The Dual-Concern Model (Applied in the Domains of Negotiation and Bargaining): How people balance their own needs with others’ needs during negotiations or bargaining.
• Equity Theory: How people want fairness in relationships and what happens when they feel things are unfair.
• Self-Expansion Approach: How people grow by learning from others and taking on new roles or responsibilities.
• Social Exchange Theory: How people give and receive things in relationships, like time, help, or support.