Useful parameters for the statistical design of trials in widening participation

The last decade or so has seen a proliferation in the use of randomised controlled trials (RCT) conducted in the education field in general, perhaps most prominently in the case of the Education Endowment Foundation, which has commissioned more than 200 such randomised trials. The same time period has also seen a growing focus in higher education (HE) institutions on widening participation in higher education. Despite significant investment by government and providers, the resources to be dedicated to this goal are scarce, leading to a growing interest in learning `what works´ for widening participation. This development has seen growth in the number of randomised trials in higher education access and participation. In this paper, we aim to support practitioners and researchers conducting trials by providing values for parameters that are essential in the design of such trials, most prominently the intra-cluster-correlation-rate.