Edgar Schein (1969, 1978, 1989, 1990) has proposed three models of consultation based on assumptions inherent in different helping styles. The first two models, purchase-of-expertise and doctor-patient, focus on the content of organizational problems. The client gives the problem to the consultant to find and implement solutions. The process consultation model focuses on how organizational problems are solved. The client and consultant collaborate throughout the problem-solving effort to find workable solutions. Because of the nature of organizations' cultures and the underlying assumptions that determine how they operate, Schein has suggested that it is most efficacious for consultants to begin in the process consultation mode and involve the client in the investigation of the problem.