Final answer:
Ronnie's interviews with prostitutes to understand their social perspectives and cultural value is an example of participant observation, a type of field research that involves collecting primary data from a natural environment.
Step-by-step explanation:
The type of field research that Ronnie engaged in by interviewing 35 prostitutes in Seattle, Washington, to understand their social perspectives and cultural value can best be described as participant observation. This method involves the researcher joining people and participating in a group's routine activities for the purpose of observing them within that context. Unlike surveys or experiments, participant observation allows the researcher to experience the subject's world firsthand and collect primary data from a natural environment.