Psychotherapy and evidence-based medicine (EBM)--randomized controlled vs. naturalistic studies: is there only one gold standard?

The present article deals with the question as to which kind of evidence is necessary to demonstrate the effectiveness of a psychotherapeutic method. The authors point out that randomized controlled studies (RCTs) are carried out in standardized laboratory contexts, whereas naturalistic studies are based on conditions in the psychotherapeutic practice. Accordingly, RCTs and naturalistic studies address different questions of research (laboratory vs. field). This view has several important implications: (1.) RCTs and naturalistic studies do not differ concerning their internal and external validity. (2.) In principal, naturalistic studies do not provide lower level evidence than RCTs. (3.) Evidence from RCTs cannot be transferred to psychotherapeutic practice in the field: If a therapy has worked in an RCT, this does not necessarily imply that it will work in the field as well. (4.) Naturalistic studies provide important evidence for determining the effectiveness of a therapy in practice. (5.) The proposed catalogues for levels of evidence focus on RCTs. Thus, they cannot be applied to hypotheses on the effectiveness of a therapy in the field (naturalistic studies). (6.) It is necessary to define separate criteria for levels of evidence of naturalistic studies. In this article, criteria and levels of evidence of naturalistic studies are defined. The implications of the differentiation of randomized controlled vs. naturalistic studies is discussed.