Effect and efficacy - on the function of models for the assessment of therapeutic efficacy.

Whilst the "effect" of a drug can be observed or deduced from observational data, the concept of "therapeutic efficacy" represents mainly a theoretical construction of a high degree of abstraction which is inconceivable without reciprocal combination with other theoretical constructs. The "therapeutic efficacy" of drugs can be investigated only via clinical-pharmacological or clinical models. Several examples are given. The strength of evidence of models is discussed as well as the necessity to continually test them empirically.