NDLI: Placebo response and effect in randomized clinical trials: meta-research with focus on contextual effects

Content Provider	Springer Nature : BioMed Central
Author	Hafliðadóttir, Sigurlaug H. Juhl, Carsten B. Nielsen, Sabrina M. Henriksen, Marius Harris, Ian A. Bliddal, Henning Christensen, Robin
Abstract	Background Contextual effects (i.e., placebo response) refer to all health changes resulting from administering an apparently inactive treatment. In a randomized clinical trial (RCT), the overall treatment effect (i.e., the post-treatment effect in the intervention group) can be regarded as the true effect of the intervention plus the impact of contextual effects. This meta-research was conducted to examine the average proportion of the overall treatment effect attributable to contextual effects in RCTs across clinical conditions and treatments and explore whether it varies with trial contextual factors. Methods Data was extracted from trials included in the main meta-analysis from the latest update of the Cochrane review on “Placebo interventions for all clinical conditions” (searched from 1966 to March 2008). Only RCTs reported in English having an experimental intervention group, a placebo comparator group, and a no-treatment control group were eligible. Results In total, 186 trials (16,655 patients) were included. On average, 54% (0.54, 95%CI 0.46 to 0.64) of the overall treatment effect was attributable to contextual effects. The contextual effects were higher for trials with blinded outcome assessor and concealed allocation. The contextual effects appeared to increase proportional to the placebo effect, lower mean age, and proportion of females. Conclusion Approximately half of the overall treatment effect in RCTs seems attributable to contextual effects rather than to the specific effect of treatments. As the study did not include all important contextual factors (e.g., patient-provider interaction), the true proportion of contextual effects could differ from the study’s results. However, contextual effects should be considered when assessing treatment effects in clinical practice. Trial registration PROSPERO CRD42019130257 . Registered on April 19, 2019.
Related Links	https://trialsjournal.biomedcentral.com/counter/pdf/10.1186/s13063-021-05454-8.pdf
Ending Page	15
Page Count	15
Starting Page	1
File Format	HTM / HTML
ISSN	17456215
DOI	10.1186/s13063-021-05454-8
Journal	Trials
Issue Number	1
Volume Number	22
Language	English
Publisher	BioMed Central
Publisher Date	2021-07-26
Access Restriction	Open
Subject Keyword	Medicine Public Health Biomedicine Statistics for Life Sciences Health Sciences Placebo response Placebo effect Contextual effects Proportional contextual effect Medicine/Public Health
Content Type	Text
Resource Type	Review
Subject	Medicine Pharmacology (medical)
Journal Impact Factor	2/2023
5-Year Journal Impact Factor	2.1/2023

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