Table 2 Summary of the factorial design of the simulation study for the primary objective

Number of clusters in each treatment arm (K)

5, 9, 13

Number of observations per cluster (M)

300

Intra-cluster correlation (ρ)

0.001, 0.01, 0.05, 0.1

Standardised treatment effect (θ)

0 or 0.5 (0.2 (13 clusters per arm),

0.25 (9 clusters per arm, ICC = 0.01 or 0.001))

Number of covariates in the data generation model (L)

4

Magnitude of prognostic effect of covariates

2

Number of covariates balanced in the randomisation (C)

1, 2, 3, 4

Candidate set

10%, 20%, …, 90% worst schemes, 100% (simple randomisation), 10%, …, 90% best schemes

Number of covariates adjusted in the analysis (A)

1, 2, 3, 4