at Duke University, despite knowing little English. Stern was the cousin of the Jewish philosopher, literary critic and theorist, Walter Benjamin. Stern died suddenly on March 27, 1938 of coronary occlusion. Academic career Stern studied at the University of Berlin under the guidance of Hermann Ebbinghaus. He received his PhD in 1893. He then taught at the University of Breslau for 19 years, from 1897 to 1916. From 1916 to 1933 he was appointed Professor of Psychology at University of Hamburg. After the rise of the Nazi Reich, he left to teach at Duke University, where he was appointed Lecturer and Professor. Major contributions Work in Child Development Stern greatly influenced the area of child development with the work he did with his wife, Clara. They used his three children, Hilde, Gunther, and Eva, as subjects, studying the development of language as well as other aspects of child development that they observed. His children were born in 1900, 1902, and 1904 respectively, and Stern and his wife started the journaling from the day each were born up until they were 12, 10, and 7, respectively. The data that they recorded included reactions, babbling, the ability to recall events, lying, moral judgement, and even systematic recording sessions where the child would elicit story narratives and descriptions with one parent while the other jotted down the notes. Through their observations Stern found what is called "game theory", which is that child's play is necessary for the personal development of a child. Intelligence Quotient During Stern's time, many other psychologists were working on ways to qualitatively assess individual differences. Alfred Binet and Théodore Simon, for instance, were developing tests to assess the mental age of children in order to identify learning disabilities, but lacked a standardized way to compare these scores across populations of children. Stern suggested a change in the formula for intelligence, which has previously been calculated using the difference between an individual's mental age and chronological age. Instead, Stern proposed dividing an individual's mental age by their chronological age to obtain a single ratio. This formula was later improved by Lewis Terman, who multiplied the intelligence quotient by 100 to obtain a whole number. Stern, however, cautioned against the use of this formula as the sole way to categorize intelligence. He believed individual differences, such as intelligence, are very complex in nature and there is no easy way to qualitatively