[The specific placebo effect]

Abstract

Placebo effects are considered a relevant component of any therapeutic intervention. At the same time clinical researchers try to control for them as if they were unspecific noise which cannot be differentiated any further. This article shows that the evidence for clinically relevant placebo effects is contradictory. The author believes that these contradictions are mainly due to the misleading terms and concepts of placebo, specific and unspecific effects. A model interpreting all effects of an intervention (excluding spontaneous changes and measurement error) as specific (having a clear-cut mechanism and a size depending on the specific conditions) is proposed. The part of the total effect caused by the postulated mechanism (the specific effect in common terms) is interpreted as attributable while the other parts are considered associated effects. The size of associated effects depends on the characteristics of interventions, patients and providers. This model would better explain the contradictory results reported in placebo research. Further implications for research and health care decision making are discussed.