Development of psychotherapists: Concepts, questions, and methods of a collaborative international study. - Orlinsky,D.E.; Ambühl,H.; Rønnestad,M.H.; Davis,J.D.; Gerin,P.; Davis,M.; Willutzki,U.; Botermans,J-F.; Dazord,A.; Cierpka,M.; Aapro,N.; Buchheim,P.; et al. (Psychother Res, 1999)