Expectancy Effect in Three Mind-Body Clinical Trials

Abstract

Expectancy, arguably the prime component of the placebo effect, has been shown to significantly modify the effects of many treatments. Furthermore, various forms of mind-body interventions have demonstrated effective improvements in outcomes. The aim of this study was to examine the relationship between pretreatment expectations and symptom reduction in a secondary analysis of 3 mind-body intervention programs. An adjusted correlation and regression analysis compared data from a 6-question expectancy questionnaire to a self-reported clinical impression of change score. Only 1 of the 6 expectancy questions in 1 of the 3 studies reached significance (B ¼ 0.087; P ¼ .025). The combined data from all 3 studies did not reveal significant expectancy effects. The positive effects of mindfulness meditation appear to be independent of an expectancy effect. The placebo effect has been thought of as either a nuisance to research or a fascinating and interdisciplinary problem in understanding the healing process.1,2 Evidence indicates that among certain conditions, placebo can have therapeutically significant effects.3 Among these conditions are pain, 12 These contradictory findings cannot be easily dismissed when one considers the difficulties of collecting data on placebo effect from clinical trials. In particular, publication bias against negative results in controlled trials would tend to suppress results showing large effects of placebo control treatments. 13 Despite its variable history, current placebo research is attempting to better understand both the mechanisms that mediate the placebo effect as well as the conditions and populations that are susceptible to it or not, with the ultimate goal of improving standards of care.A useful consideration in understanding the placebo effect is the biocultural model. In that theory, there was once an evolutionary selective pressure to believe in the healing powers of shaman and/or supernatural phenomena.14 This model suggests that making a bigger show (ie, more elaborate procedure) will have a more profound effect resulting in greater optimism and survival. Supporting this theory is the fact that more invasive procedures seem to have greater effect than less invasive, 15 placebo surgery is more effective than placebo pills, capsules are better than tablets, and bigger and brighter colored pills are better than smaller and dull colored pills.16 Furthermore, this model accounts for studies that demonstrate that longer and more empathetic personal interactions with health professionals giving a placebo treatment produce a larger placebo response when compared to the same placebo treatment with minimal interaction.11 This is known as the Hawthorne effect and may account for smaller studies with fewer participants reporting greater placebo response than larger studies and why study participants may exhibit response bias, which is a tendency to self-report better results because of psychosocial expectations.17 While a detailed review of the physiological role of the placebo...

Prior Prognostic Expectations as a Potential Predictor in Neurofeedback Training

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