[Problems and pitfalls in controlled clinical studies (author's transl)].

The problems encountered in prospective clinical trials are discussed: knowledge of the literature, precise formulation of the question answering the problem, number and qualifications of patients, duration of the trial, parameters to be measured. A surgical trial can hamper the education of the residents, or it can be devaluated by incompetent surgeons. Patients do not come for follow-up for several reasons (change of domicile, absence of disturbances, disagreeable tests).