What diagram illustrates cause and effect relationships?

The interrelationship diagram is the correct choice as it effectively illustrates cause and effect relationships. This type of diagram is used to map out and visualize the connections between various factors or variables, helping teams identify links between causes and their potential effects. By laying out these relationships, the interrelationship diagram allows for a clearer understanding of how different elements influence one another, which can lead to more focused problem-solving and root cause analysis.

In contrast, the other diagram types each serve specific purposes that don't primarily center on cause and effect. For instance, a process decision program chart helps in planning for likely outcomes based on various decision paths, focusing more on decision-making paths than direct causal relationships. The tree diagram is utilized for hierarchical breakdowns of information or processes, primarily focusing on classification and structuring, rather than direct cause-effect connections. Lastly, the affinity diagram organizes a large number of ideas into their natural relationships, facilitating brainstorming and categorization but not explicitly mapping cause and effect.