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Non-randomized clinical studies (case series and cohort studies) are often subject to bias. Maximum validity should be achieved in performing randomized controlled trials (RCTs). The term ‘validity’ consists of three components: formal correctness (internal validity), clinical relevance (external validity), and suitability (content validity). Suitability is achieved if an RCT is adapted to complementary medical demands and if the complementary therapy is executed according to the state of the art. Double-blind RCTs might be subject to a compensatory placebo effect, giving rise to false-negative results. Nevertheless, this is not an argument against RCTs, because RCTs are not necessarily executed in a double-blind manner. However, in every RCT at least patient selection and outcome evaluation should be blinded. The RCT can prevent bias and convince potential readers and critics of the reliability of the investigation. © 1994 S. Karger GmbH, Freiburg.

Original publication




Journal article


Forschende Komplementarmedizin

Publication Date





166 - 176