What type of data collection method was used by Humphreys?

Humphreys is known for utilizing participant observation and structured interviews in his research, particularly noted in his study of the behavior of men engaging in homosexual activity in public restrooms. This method allowed him to immerse himself in the social context he was studying and gather rich, qualitative data through direct observation and interaction. Participant observation enables researchers to gain insights into the behaviors, attitudes, and experiences of individuals within their natural settings, thus providing depth to the findings.

Structured interviews complement this approach by offering a systematic way to collect data while still allowing for personal interaction. This method facilitates the gathering of comparable data across different participants, helping to ensure that the findings can be analyzed more rigorously. Together, these methods provide a comprehensive view of the subjects in their real-life context, highlighting the significance of understanding nuanced social behaviors.

Other methods listed, such as case studies, surveys, and longitudinal observational studies, while valuable in their own right, do not accurately represent the combination of techniques that Humphreys implemented in his notable work. Thus, the answer highlighting participant observation and structured interviews captures the essence of his methodological approach effectively.