Which theory utilizes a qualitative approach to study changing complex relationships in social systems?

Complexity theory is the correct choice because it specifically focuses on understanding and analyzing systems that exhibit intricate and often unpredictable interactions among their components. This theory is founded on the idea that social systems are not only complex due to the number of elements and their interconnections but also because these systems are adaptive and evolve over time.

Using a qualitative approach, complexity theory allows researchers to explore how these relationships change and how they are influenced by various factors, such as environment, behaviors, and interactions within the system. This method provides deeper insights into the dynamic nature of social phenomena, enabling a comprehensive understanding of how collective behaviors emerge from individual actions.

In contrast, other theories like chaos theory primarily focus on nonlinear dynamics and predictability, systems theory adheres to more structured analytical frameworks without emphasizing qualitative change, and dynamic theory centers on changes over time but may not delve into the complexities of social interactions as comprehensively as complexity theory does.