Impact of allocation concealment on conclusion drawn from meta-analyses of randomized trials

IT University of Copenhagen, København, Capital Region, Denmark
International Journal of Epidemiology (Impact Factor: 9.18). 09/2007; 36(4). DOI: 10.1093/ije/dym087
Source: OAI


Background Randomized trials without reported adequate allocation concealment have been shown to overestimate the benefit of experimental interventions. We investigated the robustness of conclusions drawn from meta-analyses to exclusion of such trials. Material Random sample of 38 reviews from The Cochrane Library 2003, issue 2 and 32 other reviews from PubMed accessed in 2002. Eligible reviews presented a binary effect estimate from a meta-analysis of randomized controlled trials as the first statistically significant result that supported a conclusion in favour of one of the interventions. Methods We assessed the methods sections of the trials in each included meta-analysis for adequacy of allocation concealment. We replicated each meta-analysis using the authors' methods but included only trials that had adequate allocation concealment. Conclusions were defined as not supported if our result was not statistically significant. Results Thirty-four of the 70 meta-analyses contained a mixture of trials with unclear or inadequate concealment as well as trials with adequate allocation concealment. Four meta-analyses only contained trials with adequate concealment, and 32, only trials with unclear or inadequate concealment. When only trials with adequate concealment were included, 48 of 70 conclusions (69%; 95% confidence interval: 56–79%) lost support. The loss of support mainly reflected loss of power (the total number of patients was reduced by 49%) but also a shift in the point estimate towards a less beneficial effect. Conclusion Two-thirds of conclusions in favour of one of the interventions were no longer supported if only trials with adequate allocation concealment were included.

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Available from: Karsten Juhl Jørgensen, Jun 24, 2014
    • "Mit dieser Methode wird demnach der Gefahr einer Verzerrung von Studienergebnissen entgegen gewirkt. Mittlerweile ist auch bekannt, dass ganze Schlussfolgerungen von Meta-Analysen falsch sein können , wenn Studien ohne randomisierten Zuordnungsprozess eingeschlossen werden (Pildal et al. 2007), dies muss jedoch nicht zwangsweise der Fall sein (Torgerson 2007). "
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    • "We extracted data on the effect of self-management interventions on health care utilisation and total costs. To assess study quality, we chose a dichotomous measure based on allocation concealment, as this is consistently associated with treatment effect [20, 21]. Allocation concealment was judged as adequate or inadequate according to the Cochrane risk of bias tool. "
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