[Studies of drugs without randomization (author's transl)].

Post marketing studies of drugs are frequently performed without randomization. In this paper the most important differences between controlled clinical trials and epidemiologic studies are discussed from a cognitive theoretical point of view. It is shown that on the transition of informations from the basic population to the document many biases may arise so that the feasibility of interpreting epidemiologic studies is doubtful. Hence, epidemiologic studies only allow us to make statements on differences between populations but not on the reasons causing them; they merely contribute to the generation of certain hypothesis on the action of drugs. These hypothesis can only be tested in experiments.