Why and for what are clinical trials the gold standard?

The epistemological basis of clinical trials and evidence-based medicine is investigated. Clinical trials are directly action-guiding experiments on treatment effects. This is the reason why well-performed clinical trials take precedence over all other types of studies as far as treatment effects are concerned. The efficiency of public health interventions can be studied with directly action-guiding experiments that have the same strong epistemic justification as clinical trials. However, in order to assess the causality of diseases, information from several types of studies will have to be combined. Here, no single type of studies has priority over all the others. Therefore, evidence hierarchies are less helpful in studies of causality than they are in investigations of the effects of treatments or interventions.