Table 2.

The number of clusters required to be randomised to each sequence of a three-sequence stepped wedge design to detect a standardised effect size of 0.1 with 80% power and two-sided significance level of 0.05.

${\rho }_d$	$r_d$	Number of clusters per sequence
$0.032$	$1$	15
$0.034$	$0.95$	16
$0.040$	$0.83$	21
$0.050$	$0.66$	29

The values of ${\rho }_d$ and $r_d$ selected are consistent with the estimate of ${\hat{\rho }}_e=0.032$ estimated in by applying the exchangeable model to the Hb1A1c outcomes in The Health Improvement Network (THIN) dataset.