whalley-inpress-consistency-NEPRINTAT

whalley-inpress-consistency-NEPRINTAT - Placebos...

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Placebos consistency 1 Consistency of the Placebo Effect Ben Whalley Michael E. Hyland School of Psychology, University of Plymouth, UK Irving Kirsch Department of Psychology, University of Hull, UK Correspondence to Michael Hyland, School of Psychology, University of Plymouth, Plymouth, PL48AA, UK. E-mail: michael. hyland@plymouth.ac.uk Key Words: Placebo effect, Placebo responders, Pain, Test-retest reliability This study received ethical approval from the University of Plymouth, Faculty of Science Research Ethics Committee.
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Placebos consistency 2 Abstract Objective: The existence of reliable personality predictors of the placebo effect is controversial. For prediction to be possible the response to placebo must be reliable. We tested the consistency of the placebo effect by assessing the response to four trials of placebo analgesic treatment. Methods: Two identical experimental pain stimuli were administered simultaneously to matching fingers on both hands. Pain sensation was compared between one finger which was treated with a placebo cream and the other which was not treated. Two placebo creams were used, each with a different label. The procedure was repeated between 1 and 8 days later using the same creams and order of presentation. Two personality traits (acquiescence and absorption) and response expectancy were assessed as potential predictors of the placebo effect. Results: Placebo effects across trials were highly correlated ( r = .60 and .77) when placebos bore the same name, but were not significantly correlated when placebos had different names. Placebo effects were significantly associated with response expectancy, but not with acquiescence or absorption. Conclusions: Context-specific predictions of placebo response (e.g., expectancy) are possible, but personality predictors will not be consistent across contexts.
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Placebos consistency 3 Introduction When placebo effects are large, it can be difficult to demonstrate drug effects in clinical trials [1,2], and this has stimulated interest in identifying responders in order that that drug-placebo differences can be more easily detected [3]. One method for doing so is to use placebo run-in or ‘washout’ periods in which all participants in a trial (including those assigned to verum) are given a placebo, usually for a period of 7 to 10 days. Following this period, participants who have responded to the placebo are excluded from the trial [4]. However, meta-analysis of antidepressant trials comparing those with a run-in period to those without one suggests that this method does not increase drug-placebo differences [5,6]. An alternative method is to identify self-report measures of individual differences that predict placebo responding. Significant correlations between placebo response and the personality trait of acquiescence have been reported [7-11]. Despite these reports, the general consensus is that reliable correlates of the placebo response have not been found [12]. Both placebo washout periods and the search for personality correlates of
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whalley-inpress-consistency-NEPRINTAT - Placebos...

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