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Table 1 Parameter estimates following homogeneous cluster merges: scenario 1 a

From: Changing cluster composition in cluster randomised controlled trials: design and analysis considerations

 

Number of cluster merges per treatment group

Empirical estimates

0

1

2

5

10

20

Intercept, β0

0.001 (−0.003, 0.005)

0.000 (−0.003, 0.004)

−0.001 (−0.005, 0.002)

−0.001 (−0.004, 0.002)

0.000 (−0.003, 0.004)

−0.003 (−0.006, 0.001)

Treatment effect, β1

0.200 (0.195, 0.205)

0.200 (0.195, 0.205)

0.201 (0.196, 0.206)

0.202 (0.198, 0.207)

0.201 (0.196, 0.206)

0.204 (0.199, 0.209)

σ b 2

0.050 (0.048, 0.051)

0.049 (0.048, 0.051)

0.047 (0.046, 0.049)

0.044 (0.043, 0.045)

0.038 (0.037, 0.040)

0.024 (0.023, 0.025)

σ w 2

0.950 (0.947, 0.952)

0.952 (0.949, 0.954)

0.954 (0.951, 0.957)

0.955 (0.953, 0.958)

0.962 (0.959, 0.965)

0.975 (0.973, 0.978)

Intracluster correlation coefficient

0.050 (0.048, 0.051)

0.049 (0.048, 0.051)

0.047 (0.046, 0.049)

0.044 (0.042, 0.045)

0.038 (0.037, 0.039)

0.024 (0.023, 0.025)

Cluster size variance

0

10.1

20.2

49.7

90.4

0

Empirical power

81.8%

80.0%

82.0%

81.7%

80.9%

83.9%

  1. aPatient outcomes are assumed to be unaffected by cluster merge. Total of 80 clusters with 20 patients in each prior to cluster merges. Data are mean (95% confidence interval). σ b 2 is the between-cluster variance and σ w 2 is the within-cluster variance.