A psychologist is conducting an in-depth study of a single individual who has a rare behavioral condition. The psychologist strongly believes this condition is caused by a specific type of social interaction in early adolescence. During interviews, the psychologist tends to ask leading questions about the individual's teenage years and interprets ambiguous statements from the individual as clear support for their initial theory, while giving less weight to other life events. What is the most significant methodological weakness demonstrated in this approach?

Evaluating a Psychological Investigation