Cluster randomized trials of individual-level interventions were at high risk of bias

Abstract

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Risk of Bias in Cluster Randomised Controlled Trials of Individual-Level Interventions: Protocol for a Semi-Structured Interview Study

“…Cluster randomised trials lend themselves by design to being at an increased risk of bias in comparison to individual randomised trials. Although there is a wealth of research in this area (Bolzern et al, 2018; Brierley et al, 2012; Diaz-Ordaz et al, 2013; Easter et al, 2021; Eldridge et al, 2008; Froud et al, 2012; Hahn et al, 2005; Puffer et al, 2003; Yang et al, 2017), alluding to the fact that it is important to address these areas at risk of bias, by designing the bias out, or implementing methods to minimise bias, to name a few, it is now even more paramount to gain a deeper level of understanding. Questions such as, “How were decisions made within the research team on designing the study?”, “What approaches were considered to minimise bias?” and “How important is it to address risk of bias in this study?” are not usually answered in such reviews of the literature.…”

“…Using these criteria, 104 eligible studies formed our sampling frame (Figure 1). For the pilot phase we will use the six most recent trials identified in an earlier review (Easter et al, 2021), limited to studies with the same inclusion criteria as the main sampling frame and ensuring there is no overlap with the main sample. These sampling frames will be used as the basis from which to identify researchers with experience in conducting cluster randomised trials of individual-level interventions.

Figure 1.Identification of trials for inclusion.

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“…A pilot phase will be completed prior to undertaking the formal semi-structured interviews, using a set of the six most recent cluster trials of individual-level interventions with active recruitment, identified from a previous review (Easter et al, 2021). Participants will be approached using the same methods as described below.…”

“…The areas that are outlined in the topic guide are recruitment (focused around selection bias) and design justification. The content of this topic guide has been informed by the risks of bias observed within the review of 40 cluster trials of individual-level interventions (Easter et al, 2021). The topic guide will be refined based on feedback from the pilot phase.…”

“…We recently identified that all but a few of a random-sample of 40 trials of individual-level interventions evaluated using a cluster randomised design were assessed at high risk of bias (Easter et al, 2021). The causes of these biases were multi-factorial, but one prominent cause was due to identification and recruitment biases.…”