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Ludger Gerdesmeyer, et al. Pain Physician 2017; 20:387-396
Randomized Placebo-Controlled Placebo Trial to Determine the Placebo Effect Size

Abstract:
Background: It is the gold standard to use a placebo treatment as the control group in
prospective randomized controlled trials (RCTs). Although placebo-controlled trials can reveal
an effect of an active treatment, the pure effect of a placebo treatment alone has never been
presented or evaluated. No evidence-based, placebo-therapeutic options are currently available,
and no placebo-controlled trials have been performed to elucidate the pure placebo effect.
Objectives: To analyze the pure placebo effect on clinical, chronic pain through a blinded RCT.
Study Design: A prospective, randomized, placebo-controlled trial.
Setting: Medical University centers.
Methods: One-hundred eighty-two patients suffering from chronic plantar heel pain for over
6 months,who failed to respond to conservative treatments, were screened and 106 of these
patients were enrolled into this study. The patients were randomly assigned to receive either a
blinded placebo shockwave treatment or an unblinded placebo shockwave treatment. The primary
outcome measure was the differences in percentage change of visual analogue scale (VAS) scores
6 weeks after the intervention. The secondary outcome measure was the differences in Roles and
Maudsley pain score (RMS) 6 weeks after intervention. As an exploratory outcome, 2-sided group
comparisons for baseline characteristics between active treatment and controls were done using
the Mann-Whitney-U tests for group comparisons; treatment efficiency was calculated by the
effect size coefficient and benchmarks for the Mann-Whitney estimator according to the t-test
of 2 independent samples for quantitative data, as well as the Fisher’s exact test for binary data.
Results: Patients from both groups did not differ with respect to heel pain ratings at baseline,
for both the VAS (P = .476) and RMS (P = .810) scores. After 6 weeks, patients receiving the
blinded placebo treatment reported less heel pain on both scales (VAS: P = .031; RMS: P = .004).
Change scores of pain ratings were significantly higher in the blinded placebo group than in the
un-blinded placebo group (VAS: P = .002; RMS: P = .002).
Limitations: As the study represents the first to use an inverse placebo RCT (IPRCT), further
conceptual and methodological issues need to be addressed to describe detailed, underlying
mechanisms. Specific contextual, intrapersonal, and interpersonal factors modulating the placebo
effects should be addressed in future IPRCTs.
Conclusion: The present study indicated that true placebo effect sizes can be analyzed through
a proper IPRCT design. Instead of treating high numbers of patients with placebos in a RCT, which
increases the risk for subjects not receiving the active treatment, the IPRCT technique seems to
be much more appropriate to analyze the effect sizes of any active treatment,