The Kaiser Foundation Hospital in Oakland, California was the site of the early development of interpersonal theory. "In the development of the interpersonal system more than 5,000 cases (psychiatric, medical, and normal controls) [were] studied and diagnosed" (Leary, 1957, p. vi). Timothy Leary was director of psychology research at the Kaiser Foundation, and the observations made by the psychology research group were compiled into Leary's magisterial (1957) book Interpersonal Diagnosis of Personality. One of the key ideas of the interpersonal theory was that interpersonal variables are arranged into a circle that later came to be known as the interpersonal circumplex.