Final answer:
Sigmund Freud developed his theory of human personality through conducting case studies, while John B. Watson focused on observable behavior and stimulus-response reactions.
Step-by-step explanation:
Sigmund Freud developed his theory of human personality through conducting case studies with a few clients over an extended period of time. Freud's research approach involved in-depth interviews and detailed analysis of individual experiences and behaviors.
On the other hand, John B. Watson was an influential psychologist who developed his theories primarily through using observable behavior and stimulus-response reactions. Watson argued that psychology should focus on outward observable behavior that can be measured, rather than internal mental processes.