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Three-armed trials including placebo and no-treatment groups may be subject to publication bias: systematic review.

Koog YH, We SR, Min BI - PLoS ONE (2011)

Bottom Line: It has been argued that placebos may not have important clinical impacts in general.All data were then analyzed for publication bias.In the simulation, the magnitude of the placebo effect was smaller than that calculated after considering publication bias.

View Article: PubMed Central - PubMed

Affiliation: Honam Research Center, Medifarm Hospital, Suncheon, Republic of Korea. samlungchim@hanmail.net

ABSTRACT

Background: It has been argued that placebos may not have important clinical impacts in general. However, there is increasing evidence of a publication bias among trials published in journals. Therefore, we explored the potential for publication bias in randomized trials with active treatment, placebo, and no-treatment groups.

Methods: Three-armed randomized trials of acupuncture, acupoint stimulation, and transcutaneous electrical stimulation were obtained from electronic databases. Effect sizes between treatment and placebo groups were calculated for treatment effect, and effect sizes between placebo and no-treatment groups were calculated for placebo effect. All data were then analyzed for publication bias.

Results: For the treatment effect, small trials with fewer than 100 patients per arm showed more benefits than large trials with at least 100 patients per arm in acupuncture and acupoint stimulation. For the placebo effect, no differences were found between large and small trials. Further analyses showed that the treatment effect in acupuncture and acupoint stimulation may be subject to publication bias because study design and any known factors of heterogeneity were not associated with the small study effects. In the simulation, the magnitude of the placebo effect was smaller than that calculated after considering publication bias.

Conclusions: Randomized three-armed trials, which are necessary for estimating the placebo effect, may be subject to publication bias. If the magnitude of the placebo effect is assessed in an intervention, the potential for publication bias should be investigated using data related to the treatment effect.

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Results of effect sizes combined over all trials, effect sizes predicted for trials from random effects meta-regression analysis with standard error  = 0, and effect sizes simulated on data from nonparametric trim and fill analysis.SE  =  standard error.
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pone-0020679-g004: Results of effect sizes combined over all trials, effect sizes predicted for trials from random effects meta-regression analysis with standard error  = 0, and effect sizes simulated on data from nonparametric trim and fill analysis.SE  =  standard error.

Mentions: Figure 4 shows the results of the pooled effect sizes of all eligible trials, the predicted effect sizes for hypothetical trials with infinite size, and the simulated effect sizes for data from non-parametric trim and fill analysis. For the treatment effect (Figure 4A and B), the effect sizes combined over eligible trials were greater than those predicted for hypothetical trials with infinite size or those simulated on data from nonparametric trim and fill analysis. For the placebo effect (Figure 4A and B), the effect sizes combined over eligible trials were smaller than those simulated on data from non-parametric trim and fill analysis, although they were included within the range of the 95% confidence interval for hypothetical placebo effect from meta-regression with standard error  = 0.


Three-armed trials including placebo and no-treatment groups may be subject to publication bias: systematic review.

Koog YH, We SR, Min BI - PLoS ONE (2011)

Results of effect sizes combined over all trials, effect sizes predicted for trials from random effects meta-regression analysis with standard error  = 0, and effect sizes simulated on data from nonparametric trim and fill analysis.SE  =  standard error.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3105112&req=5

pone-0020679-g004: Results of effect sizes combined over all trials, effect sizes predicted for trials from random effects meta-regression analysis with standard error  = 0, and effect sizes simulated on data from nonparametric trim and fill analysis.SE  =  standard error.
Mentions: Figure 4 shows the results of the pooled effect sizes of all eligible trials, the predicted effect sizes for hypothetical trials with infinite size, and the simulated effect sizes for data from non-parametric trim and fill analysis. For the treatment effect (Figure 4A and B), the effect sizes combined over eligible trials were greater than those predicted for hypothetical trials with infinite size or those simulated on data from nonparametric trim and fill analysis. For the placebo effect (Figure 4A and B), the effect sizes combined over eligible trials were smaller than those simulated on data from non-parametric trim and fill analysis, although they were included within the range of the 95% confidence interval for hypothetical placebo effect from meta-regression with standard error  = 0.

Bottom Line: It has been argued that placebos may not have important clinical impacts in general.All data were then analyzed for publication bias.In the simulation, the magnitude of the placebo effect was smaller than that calculated after considering publication bias.

View Article: PubMed Central - PubMed

Affiliation: Honam Research Center, Medifarm Hospital, Suncheon, Republic of Korea. samlungchim@hanmail.net

ABSTRACT

Background: It has been argued that placebos may not have important clinical impacts in general. However, there is increasing evidence of a publication bias among trials published in journals. Therefore, we explored the potential for publication bias in randomized trials with active treatment, placebo, and no-treatment groups.

Methods: Three-armed randomized trials of acupuncture, acupoint stimulation, and transcutaneous electrical stimulation were obtained from electronic databases. Effect sizes between treatment and placebo groups were calculated for treatment effect, and effect sizes between placebo and no-treatment groups were calculated for placebo effect. All data were then analyzed for publication bias.

Results: For the treatment effect, small trials with fewer than 100 patients per arm showed more benefits than large trials with at least 100 patients per arm in acupuncture and acupoint stimulation. For the placebo effect, no differences were found between large and small trials. Further analyses showed that the treatment effect in acupuncture and acupoint stimulation may be subject to publication bias because study design and any known factors of heterogeneity were not associated with the small study effects. In the simulation, the magnitude of the placebo effect was smaller than that calculated after considering publication bias.

Conclusions: Randomized three-armed trials, which are necessary for estimating the placebo effect, may be subject to publication bias. If the magnitude of the placebo effect is assessed in an intervention, the potential for publication bias should be investigated using data related to the treatment effect.

Show MeSH