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In randomized clinical trials, the overall treatment effect can be viewed as a combination of the intervention’s specific effect and contextual effects. This meta-research synthesizes eligible placebo-controlled RCTs across clinical conditions to estimate the average proportional contribution of contextual effects and assess variation with trial contextual factors.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":40,"@type":76,"position":81},"https://docshare.wps.com/document/research-report/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/placebo-response-and-effect-in-randomized-clinical-trials-meta-research-with-focus-on-contextual-effects/137799/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/placebo-response-and-effect-in-randomized-clinical-trials-meta-research-with-focus-on-contextual-effects/137799.png","ImageObject",300,407,{"name":92,"@type":93},"Lucas Martin","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-09-19","2026-08-23",true,{"@type":102,"interactionType":103,"userInteractionCount":34},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"What are contextual effects in randomized clinical trials?","Question",{"text":112,"@type":113},"Contextual effects refer to all health changes resulting from administering an apparently inactive treatment, which includes the placebo response. They capture the impact of expectations, emotions, and the clinical context.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"How was the meta-research conducted in this study?",{"text":117,"@type":113},"Trials were extracted from studies included in a Cochrane review update on placebo interventions across clinical conditions. Eligible studies were randomized clinical trials reported in English with an experimental group, a placebo comparator, and a no-treatment control group.",{"name":119,"@type":110,"acceptedAnswer":120},"What proportion of the overall treatment effect was attributed to contextual effects?",{"text":121,"@type":113},"Across 186 trials (16,655 patients), contextual effects accounted for an average of 54% of the overall treatment effect. The study also reports that contextual effects were higher under certain trial design features such as blinded outcome assessment and concealed allocation.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},137799,1787447648,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":39,"category_name":40,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":34,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":139,"language":140,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":141,"faqs":142,"seo_title":143,"seo_description":67,"update_tm":129,"read_time":144},8796095360427,"https://ap-avatar.wpscdn.com/davatar_994ba38a5ba835b3df7d355c54d3ed8d","Hafliðadóttir et al. Trials (2021) 22:493 [https://doi.org/10.1186/s13063-021-05454-8](https://doi.org/10.1186/s13063-021-05454-8)  \nREVIEW Open Access   \nPlacebo response and effect in randomized clinical trials: meta-research with focus on contextual effects  \nSigurlaug H. Hafliðadóttir 1,2, Carsten B. Juhl2,3, Sabrina M. Nielsen 1,4, Marius Henriksen5, Ian A. Harris6,7,8, Henning Bliddal5 and Robin Christensen 1,4*  \nAbstract  \nBackground: 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 posttreatment 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.  \nMethods: 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.  \nResults: 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.  \nConclusion: 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.  \nTrial registration: PROSPERO CRD42019130257 . Registered on April 19, 2019 .  \nKeywords: Placebo response, Placebo effect, Contextual effects, Proportional contextual effect  \n* Correspondence: [Robin.Christensen@regionh.dk](Robin.Christensen@regionh.dk)  \n1Section for Biostatistics and Evidence-Based Research, the Parker Institute, Bispebjerg and Frederiksberg Hospital, Nordre Fasanvej 57, DK-2000  \nCopenhagen F, Denmark  \n4Research Unit of Rheumatology, Department of Clinical Research, University of Southern Denmark, Odense University Hospital, Odense, Denmark  \nFull list of author information is available at the end of the article  \n© The Author(s) . 2021 Open Access This article is licensed under a Creative Commons Attribution 4 . 0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit [http://creativecommons.org/licenses/by/4.0/](http://creativecommons.org/licenses/by/4.0/) . The Creative Commons Public Domain Dedication waiver ([http://creativecommons.org/publicdomain/zero/1.0/](http://creativecommons.org/publicdomain/zero/1.0/)) ","cbCaifNxdyuzEedm","https://ap.wps.com/l/cbCaifNxdyuzEedm","pdf",1070862,15,"English","# Abstract\n## Background\n## Methods\n## Results\n## Conclusion\n## Trial registration\n## Keywords\n# Background\n## Therapeutic environment and placebo response","[{\"question\":\"What are contextual effects in randomized clinical trials?\",\"answer\":\"Contextual effects refer to all health changes resulting from administering an apparently inactive treatment, which includes the placebo response. They capture the impact of expectations, emotions, and the clinical context.\"},{\"question\":\"How was the meta-research conducted in this study?\",\"answer\":\"Trials were extracted from studies included in a Cochrane review update on placebo interventions across clinical conditions. Eligible studies were randomized clinical trials reported in English with an experimental group, a placebo comparator, and a no-treatment control group.\"},{\"question\":\"What proportion of the overall treatment effect was attributed to contextual effects?\",\"answer\":\"Across 186 trials (16,655 patients), contextual effects accounted for an average of 54% of the overall treatment effect. The study also reports that contextual effects were higher under certain trial design features such as blinded outcome assessment and concealed allocation.\"}]","Placebo response and effect in randomized clinical trials - meta-research with focus on contextual effects | PDF",38]