Answer:
Past Experience
Step-by-step explanation:
Professor conducts the study on a tip given by the customer to the waiter with the observation and own experience working in a restaurant with a specific behavior which includes the posture and communication. when a professor working in the restaurant he has been observed the behavior of the customer and gets an initial idea to observe the behavior of the people and find out the reason behind this specific behavior. the researcher used his experience and applied it to another population to know the specific behavior of people. the researcher used here the applied research.