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Table 1 Comparison of t-test, mixed model for repeated measures with compound symmetric variance-covariance, and mixed model for repeated measures with unstructured variance-covariance, with respect to bias percent and power; simulation results for linear trajectory

From: Single time point comparisons in longitudinal randomized controlled trials: power and bias in the presence of missing data

  ρ = 0.7 ρ = 0.5 ρ = 0.3
  (N = 10,000) (N = 10,000) (N = 10,000)
  Bias % Power Bias % Power Bias % Power
Complete       
 t-testa 0 80 0 80 0 80
 MMRM-CSb 0 80 0 81 0 80
 MMRM-UNc 0 80 0 80 0 80
MCAR with equal dropout of 40 % in each group     
t-test 0 58 0 58 0 58
 MMRM-CS 0 70 0 65 0 61
 MMRM-UN 0 70 0 65 0 60
MAR with unequal dropout of 30 % and 50 % in each group, one reason
t-test −15 44 −11 48 −6 51
 MMRM-CS 0 69 0 64 0 60
 MMRM-UN 0 69 0 64 0 59
MAR with unequal dropout of 30 % and 50 % in each group, two reasons
t-test −5 53 −3 53 −2 54
 MMRM-CS 0 68 0 63 0 59
 MMRM-UN 0 68 0 62 0 59
MAR with equal dropout of 40 % in each group
t-test −1 57 0 57 −1 56
 MMRM-CS 0 69 0 64 0 59
 MMRM-UN 0 69 0 64 0 59
MNAR with unequal dropout of 30 % and 50 % in each group, one reason
t-test −18 42 −16 43 −15 44
 MMRM-CS −6 64 −9 56 −13 49
 MMRM-UN −6 64 −9 56 −13 49
MNAR with unequal dropout of 30 % and 50 % in each group, two reasons
t-test −7 52 −6 51 −6 51
 MMRM-CS −2 67 −4 60 −5 54
 MMRM-UN −2 67 −4 60 −5 55
MNAR with equal dropout of 40 % in each group
t-test −3 55 −3 55 −3 55
 MMRM-CS −1 69 −2 63 −2 58
 MMRM-UN −1 69 −2 63 −2 58
  1. aIndependent two-sample t-test for the difference between group means at the final time point
  2. bMixed model for repeated measures, compound symmetric variance-covariance matrix, contrast between group means at the final time point
  3. cMixed model for repeated measures, unstructured variance-covariance matrix, contrast between group means at the final time point