The placebo effect: Still under a cloud of confusion. Comments on the update by J.-M. Berthelot

The Psychological Dimensions of Placebo-Studies

Abstract. The placebo effect involves a complex network of psychological variables that are often disregarded by studies enquiring into this effect. It is hence little surprising that these psychological variables confound study outcomes and that experiments investigating the placebo effect often yield radically different results. The current article identifies three categories of psychological and methodological factors that are not systematically considered in placebo research: psychological confounds (Hawthorne effects and demand effects); methodological and data-analysis issues; and clinicians’ expectancy effects. These factors are not necessarily to be seen as mere artifacts, however, because they may constitute favorable components of the placebo effect. A set of benchmark criteria is therefore proposed to allow researchers to capitalize on these components during placebo research rather than have their results confounded by them; and to allow for a more reliable interpretation of study outcomes.