Perceived treatment, feedback, and placebo effects in double-blind RCTs: an experimental analysis

Colagiuri, Ben; Boakes, Robert A.

doi:10.1007/s00213-009-1743-9

Cited by 38 publications

(44 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, it is not easy for investigators to interpret the results of blinding assessments because the basis and the effects of suspecting which treatment has been assigned are complex. Expectation of receiving an active treatment may improve its perceived efficacy [7,23,24], and, conversely, clinical improvement may also cause trial participants to believe that they were receiving active treatment [25]. However, our finding of a positive correlation between unblinding and effect size (fig.…”

Section: Discussioncontrasting

confidence: 56%

Systematic Review of Blinding Assessment in Randomized Controlled Trials in Schizophrenia and Affective Disorders 2000-2010

Baethge¹,

Paul²,

Baldessarini³

2013

Psychother Psychosom

View full text Add to dashboard Cite

Background: Blinding is an integral part of many randomized controlled trials (RCTs). However, both blinding and blinding assessment seem to be rarely documented in trial reports. Method: Systematic review of articles on RCTs in schizophrenia and affective disorders research during 2000-2010. Results: Among 2,467 publications, 61 (2.5%; 95% confidence interval: 1.9-3.1%) reported assessing participant, rater, or clinician blinding: 5/672 reports on schizophrenia (0.7%; 0.3-1.6%) and 33/1,079 (3.1%; 2.1-4.2%) on affective disorders, without significant trends across the decade. Rarely was blinding assessed at the beginning, in most studies assessment was at the end. Proportion of patients' and raters' correct guesses of study arm averaged 54.4 and 62.0% per study, with slightly more correct guesses in treatment arms than in placebo arms. Three fourths of responders correctly guessed that they received the active agent. Blinding assessment was more frequently reported in papers on psychotherapy and brain stimulation than on drug trials (5.1%, 1.7-11.9%, vs. 8.3%, 4.3-14.4%, vs. 2.1%, 1.5-2.8%). Lack of assessment of blinding was associated with: (a) positive findings, (b) full industrial sponsorship, and (c) diagnosis of schizophrenia. There was a moderate association of treatment success and blinding status of both trial participants (r = 0.51, p = 0.002) and raters (r = 0.55, p = 0.067). Many RCT reports did not meet CONSORT standards regarding documentation of persons blinded (60%) or of efforts to match interventions (50%). Conclusions: Recent treatment trials in major psychiatric disorders rarely reported on or evaluated blinding. We recommend routine documentation of blinding strategies in reports.

show abstract

Section: Discussioncontrasting

confidence: 56%

Systematic Review of Blinding Assessment in Randomized Controlled Trials in Schizophrenia and Affective Disorders 2000-2010

Baethge¹,

Paul²,

Baldessarini³

2013

Psychother Psychosom

View full text Add to dashboard Cite

show abstract

“…While this leaves open the possibility that cultural differences are driving the difference between the active and passive studies, we doubt cultural differences would account for the 7-fold increase in the training effect, especially since the non-USA studies were primarily conducted in Westernized cultures (e.g., Europe). as performance on cognitive tasks (Colagiuri & Boakes, 2010; see also Boot et al, 2013). Given the prevalence of placebo effects, the discrepancy in findings between active and passive experimental designs cannot simply be described as a moderation effect; it has to be fully considered as a possible root cause of the effect.…”

Section: Discussionmentioning

confidence: 97%

Reevaluating the effectiveness of n-back training on transfer through the Bayesian lens: Support for the null

2015

View full text Add to dashboard Cite

A recent meta-analysis by Au et al. Psychonomic Bulletin & Review, 22, 366-377, (2015) reviewed the n-back training paradigm for working memory (WM) and evaluated whether (when aggregating across existing studies) there was evidence that gains obtained for training tasks transferred to gains in fluid intelligence (Gf). Their results revealed an overall effect size of g = 0.24 for the effect of n-back training on Gf. We reexamine the data through a Bayesian lens, to evaluate the relative strength of the evidence for the alternative versus null hypotheses, contingent on the type of control condition used. We find that studies using a noncontact (passive) control group strongly favor the alternative hypothesis that training leads to transfer but that studies using active-control groups show modest evidence in favor of the null. We discuss these findings in the context of placebo effects.

show abstract

“…In contrast, Berna et al’s (2017) use of a balanced active placebo is distinct because it does not contain a natural history group. The equivalent cell in their design is placebo treatment given under double-blind instructions, which has been shown to induce placebo effects (Colagiuri & Boakes, 2010; Kam-Hansen et al, 2014; Pollo et al, 2001). Their design means that an absence of a main effect of the analgesic does not necessarily mean that the treatment had no “absolute” effect (i.e., relative to natural history).…”

Section: Implications and Limitationsmentioning

confidence: 99%

Placebo and Active Treatment Additivity in Placebo Analgesia: Research to Date and Future Directions

Coleshill

Sharpe

Colloca

et al. 2018

International Review of Neurobiology

Self Cite

View full text Add to dashboard Cite

Placebo analgesia is a robust experimental and clinical phenomenon. While our understanding of the mechanisms of placebo analgesia has developed rapidly, some central questions remain unanswered. Among the important questions is how placebo anal-gesia interacts with active analgesic effects. It is an assumption underlying double-blind randomized placebo-controlled trials (RCTs) that the true effect of a treatment can be determined by examining the effect of the active treatment arm and subtracting the response in the placebo group (“the assumption of additivity”). However, despite the importance of this assumption for the interpretation of RCTs, it has rarely been formally examined. This article reviews the assumption of additivity in placebo analgesia by examining studies employing factorial designs manipulating both the receipt of an active analgesic and instructions about the treatment being delivered. In reviewing the literature, we identified seven studies that allowed a test of additivity. Of these, four found evidence against additivity, while the remaining three studies found results consistent with additivity. While the limited available data are somewhat mixed, the evidence suggests that at least under some conditions the assumption of additivity does not hold in placebo analgesia. The concordance between mechanisms of the active analgesic and placebo analgesia may influence whether additivity occurs or not. However, more research using factorial designs is needed to disentangle the relationship between placebo analgesia and the active effect of analgesic treatments.

show abstract

Perceived treatment, feedback, and placebo effects in double-blind RCTs: an experimental analysis

Abstract: These results indicate the importance of assessing participants' beliefs about their treatment allocation in real double-blind RCTs and considering if and how these may have affected the trial's outcome.

Cited by 38 publications

References 26 publications

Systematic Review of Blinding Assessment in Randomized Controlled Trials in Schizophrenia and Affective Disorders 2000-2010

Systematic Review of Blinding Assessment in Randomized Controlled Trials in Schizophrenia and Affective Disorders 2000-2010

Reevaluating the effectiveness of n-back training on transfer through the Bayesian lens: Support for the null

Placebo and Active Treatment Additivity in Placebo Analgesia: Research to Date and Future Directions

Contact Info

Product

Resources

About