A researcher wants to conduct an in-depth investigation into the psychological and cognitive development of a single child who was discovered living in the wild, with no prior human contact. The goal is to gather as much detailed information as possible about this unique individual's experience. Which of the following research methods would be the most appropriate and effective for this specific goal?

A researcher is deciding on a method for a new psychological study. For which of the following research questions would the in-depth study of a single, unique individual provide the most valuable and insightful data?