The P value as the guardian of medical truth -- illusion or reality?

Most medical procedures are based on scientific investigations. Such investigations hinge on the demonstration of causal relationships and therefore the principle of causality. This paper shows that neither philosophy nor the much praised value is in a position to prove that causal relationships exist. The value is able to define the precision of measurements by quantifying the random error and to demonstrate statistical relationships. For the purposes of everyday practice, conclusions can only be drawn on statistical tests based on the value with the help of intuition, deductive and inductive reasoning, belief and social consensus.