After joining the staff of the Burghölzli Mental Hospital in 1900, Jung developed and applied word-association tests for studying normal and abnormal psychology. Between 1904 and 1907, he published nine studies on these experiments. features these studies, as well as two lectures on the association method that Jung gave in 1909 when he and Freud were invited to Clark University in Worcester, Massachusetts, and three articles on psychophysical researches. Jung's word-association studies are a significant phase in the development of his thought and an important contribution to diagnostic psychology and psychiatry.