TABLE 4.

Type I error and power (%) for the interaction test across simulation scenarios comparing an analysis based on the randomisation strata and the true strata when the treatment by covariate interaction effect is of interest, the covariate effect is strong (${\beta }_X=1$) and all stratification errors are discovered.

		Type I error (%) (${\beta }_{\mathit{TX}}=0$)		Power (%) (${\beta }_{\mathit{TX}}=0.2$)		Power (%) (${\beta }_{\mathit{TX}}=0.4$)
Stratification error rate	Errors across strata	Randomisation strata	True strata a	Randomisation strata	True strata a	Randomisation Strata	True strata a
1%	Equal	5.16	5.08	33.77	34.98	86.45	88.21
1%	Unequal	4.71	5.16	33.61	35.40	86.89	88.61
20%	Equal	4.99	5.23	13.70	35.01	40.08	88.22
20%	Unequal	4.51	5.11	13.23	34.43	41.80	88.93

Note: The maximum Monte Carlo standard error across all methods and scenarios was 0.22 for type I error and 0.49 for power.

^a Matches the updated strata in this setting where all stratification errors are discovered.