Statistical efficiency
ANASTOMOTIC LEAK
An incomplete stepped wedge design was chosen in order to improve statistical efficiency by reducing both the number of clusters and the burden of individual-level data collection over all clusters necessary to achieve the required power [The EAGLE trial was designed to detect what was judged to be a clinically important, absolute reduction in anastomotic leak rate from 8.1 to 5.6% (relative risk reduction 30%), based on the leak rate in previous research as above [We also calculated that if we had used a more conventional, parallel groups cluster randomised design, with data collection in both periods in all clusters, we would have needed 358 clusters with data on 7,160 surgical procedures in total, thus demonstrating the superior efficiency of the dog-leg design.