Development of a standardised set of metrics for monitoring site performance in multicentre randomised trials: a Delphi study oleh Diane Whitham, Julie Turzanski, Lucy Bradshaw, Mike Clarke, Lucy Culliford, Lelia Duley, Lisa Shaw, Zoe Skea, Shaun P. Treweek, Kate Walker, Paula R. Williamson, Alan A. Montgomery, On behalf of the Site Performance Metrics for Multicentre Randomised Trials Collaboration