Randomisation to protect against selection bias in healthcare trials

Abstract

The results of randomised and non-randomised studies sometimes differed. In some instances non-randomised studies yielded larger estimates of effect and in other instances randomised trials yielded larger estimates of effect. The results of controlled trials with adequate and inadequate/unclear concealment of allocation sometimes differed. When differences occurred, most often trials with inadequate or unclear allocation concealment yielded larger estimates of effects relative to controlled trials with adequate allocation concealment. However, it is not generally possible to predict the magnitude, or even the direction, of possible selection biases and consequent distortions of treatment effects from studies with non-random allocation or controlled trials with inadequate or unclear allocation concealment.

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Affiliated Institutions

• Nasjonalt Kunnskapssenter for Helsetjenesten
• University of Basel CH
• McMaster University CA
• University Hospital of Basel CH
• American University of Beirut LB
• University of Modena and Reggio Emilia IT
• Carl von Ossietzky Universität Oldenburg DE

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