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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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Difference in effect sizes between large trials with at least 100 patients per arm and small trials with fewer than 100 patients.ES  =  effect size.
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pone-0020679-g002: Difference in effect sizes between large trials with at least 100 patients per arm and small trials with fewer than 100 patients.ES  =  effect size.

Mentions: When small and large trials were compared for treatment effect (Figure 2), the difference in effect sizes between large and small trials was statistically significant in acupuncture (P = 0.009) and acupoint stimulation (P = 0.0005). For acupuncture, small trials showed more benefits by 0.39 (0.10 to 0.68) in effect size than large trials, and for acupoint stimulation, more benefits by 0.64 (0.28 to 0.99) in effect size. However, there was no significant difference between small and large trials in TENS. The summary difference of −0.37 (−0.69 to −0.05) over the three interventions was statistically significant. When small and large trials were compared for placebo effect, a significant difference was found only in the acupoint stimulation (P = 0.004). The summary difference of −0.06 (−0.25 to 0.13) was not statistically significant.


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)

Difference in effect sizes between large trials with at least 100 patients per arm and small trials with fewer than 100 patients.ES  =  effect size.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0020679-g002: Difference in effect sizes between large trials with at least 100 patients per arm and small trials with fewer than 100 patients.ES  =  effect size.
Mentions: When small and large trials were compared for treatment effect (Figure 2), the difference in effect sizes between large and small trials was statistically significant in acupuncture (P = 0.009) and acupoint stimulation (P = 0.0005). For acupuncture, small trials showed more benefits by 0.39 (0.10 to 0.68) in effect size than large trials, and for acupoint stimulation, more benefits by 0.64 (0.28 to 0.99) in effect size. However, there was no significant difference between small and large trials in TENS. The summary difference of −0.37 (−0.69 to −0.05) over the three interventions was statistically significant. When small and large trials were compared for placebo effect, a significant difference was found only in the acupoint stimulation (P = 0.004). The summary difference of −0.06 (−0.25 to 0.13) was not statistically significant.

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