Why might a researcher choose a quasi-experimental design over a true experimental design?

A researcher might choose a quasi-experimental design over a true experimental design primarily because quasi-experimental designs are appropriate when random assignment to groups is not feasible. This situation often occurs in real-world settings where it is impractical or unethical to assign participants randomly. For example, when studying the effects of a particular educational program in an existing classroom, it wouldn't be ethical to randomly assign students to different classes. Instead, researchers can make use of existing groups, allowing them to evaluate the outcomes of the program without the constraints of random assignment.

In contrast, true experimental designs rely heavily on random assignment, which is crucial for establishing causal relationships. When random assignment is not practical due to ethical or logistical constraints, researchers turn to quasi-experimental designs, which can still provide valuable insights, even though they may have more limitations regarding causal inference due to potential confounding variables. This makes option D the most appropriate choice, reflecting the reality that researchers often have to work with the resources and situations available to them.