Answer : An individual's privacy.
Explanation : When a psychologist is making a determination regarding whether or not a study is ethical, one should first consider an individual's privacy versus the demand or desire for increased knowledge in a particular field of study.
Confidentiality is an important factor when dealing with studies related or specific case studies of a particular patient. After consideration of that individual's privacy he can define the ethical ways of the study to increase the knowledge in any field of study.