Final answer:
Dr. Fletcher may not conduct a true experiment due to ethical concerns, as random assignment in the context of joining a fraternity/sorority may cause psychological harm or undue pressure to participants.
Step-by-step explanation:
If Dr. Fletcher is interested in a causal relationship between joining a fraternity/sorority and attractiveness/appearance concern, he may choose not to conduct a true experiment due to ethical concerns. In a true experiment, a researcher would have to randomly assign participants to join a fraternity/sorority or not, which could lead to potential psychological harm or undue pressure to the participants. This would conflict with the ethical guidelines that protect study participants from harm. For instance, the same ethical concerns prevent experimenters from assigning participants to a scenario where they would have to experience abuse to study its effects on self-esteem.
Moreover, true experiments often require random assignment to eliminate the influences of lurking variables and establish a clear causal relationship. However, in the context of joining a fraternity/sorority, such random assignment is not practical or ethical, as individuals have the right to choose their own social affiliations and experiences.