The randomisation occurs before the start of the trial. All clusters start the trial in a control phase with no intervention being delivered at any site, then sequentially cross over from the control group to the intervention group, until all sites are receiving the intervention. Outcomes are measured on the study participants in all clusters at every time period, hence measurement of outcomes takes place at each step in the wedge; each cluster provides data points in the control and intervention conditions allowing each site to act as its own control.