ABSTRACT
In order to gain acceptance in clinical practice today all new technologies, therapeutic devices,
drugs, operations and interventional procedures must pass through a number of phases of
evaluation to establish their safety and efficacy. Although cumbersome, this process makes
sense not only in the interests of patient safety but also to ensure proper use of limited heath-
care resources. The different phases of evaluation generate standards of proof that correspond
approximately to the well-known and accepted Levels of Scientific Evidence (1). This is a
hierarchical system with anecdotal case reports at the bottom of the scale and meta-analysis
of randomized trials at the top.While clinical scientists naturally aspire to the highest standards
of proof, it is self-evident that this cannot often be achieved in one step from the inception of a
new therapeutic concept. Progression from one phase to the next, starting at the bottom is the
logical way to proceed.
