Partly in response to a study by Daniel Levinson, research in the 1970s led some women and African Americans to question whether the classic "white male" model was available or customary for people who are newcomers in traditionally white male organizations. In 1978 Edgar Schein described multiple roles for successful mentors. He identified seven types of mentoring roles in his book "Career Dynamics: Matching individual and organizational needs" (1978). He said that some of these roles require the teacher to be, for example, an "opener of doors, protector, sponsor and leader".