Table 1 Study Characteristics a
From: Ideal vs. real: a systematic review on handling covariates in randomized controlled trials
Study Characteristic | Overall | 2009 | 2014 | p-value b | |
|---|---|---|---|---|---|
Type of Study | Superiority | 255 (86) | 110 (84) | 145 (87) | 0.3047 |
Non-Inferiority | 23 (8) | 9 (7) | 14 (8) | ||
Other | 20 (7) | 12 (9) | 8 (5) | ||
Cluster-Randomized | No | 277 (93) | 117 (89) | 160 (96) | 0.0297 |
Yes | 21 (7) | 14 (11) | 7 (4) | ||
Number of Arms | 2 | 236 (79) | 107 (82) | 129 (77) | 0.5970 |
3 | 24 (8) | 8 (6) | 16 (10) | ||
4 | 26 (9) | 12 (9) | 14 (8) | ||
5 or more | 12 (4) | 4 (3) | 8 (5) | ||
Multicenter Study | Single Center | 24 (8) | 15 (11) | 9 (5) | 0.0563 |
Multicenter | 274 (92) | 116 (89) | 158 (95) | ||
Number of Centers | 22 (5–71) | 20 (4–68) | 24 (6–76) | 0.6291 | |
Number of Subjects | 556 (242–1408) | 700 (279–1888) | 457 (222–1224) | 0.0770 | |
Length of Study, Years (if reported) | 3 (2–5) | 3 (2–5) | 3 (2–5) | 0.6667 | |
Months of Subject Follow-up (if reported) | 12 (4–20) | 12 (4–22) | 12 (4–19) | 0.8274 | |
Study Initiation Year | Before 2000 | 17 (6) | 13 (10) | 4 (2) | <.0001 |
2004–2005 | 75 (26) | 66 (52) | 9 (5) | ||
2005–2009 | 123 (42) | 48 (38) | 75 (45) | ||
2010 and later | 78 (27) | 0 (0) | 78 (47) | ||
Primary Outcome | Continuous | 89 (30) | 42 (32) | 47 (28) | 0.2663 |
Binary | 113 (38) | 42 (32) | 71 (43) | ||
Time-to-Event | 84 (28) | 40 (31) | 44 (26) | ||
Other | 12 (4) | 7 (5) | 5 (3) | ||
Randomization Indicated in Title | No | 94 (32) | 40 (31) | 54 (32) | 0.7398 |
Yes | 204 (68) | 91 (69) | 113 (68) | ||
Allocation Method | Purely random allocation | 4 (1) | 3 (2) | 1 (1) | 0.1660 |
Blocked (Permuted or Random block) | 24 (8) | 9 (7) | 15 (9) | ||
Stratified or Stratified block | 205 (69) | 82 (63) | 123 (74) | ||
Minimization/Covariate-adaptive method | 32 (11) | 18 (14) | 14 (8) | ||
Other | 4 (1) | 2 (2) | 2 (1) | ||
Unable to determine | 29 (10) | 17 (13) | 12 (7) | ||
Covariate(s) Included in Allocation | No | 27 (9) | 12 (9) | 15 (9) | 0.3278 |
Yes | 241 (81) | 102 (78) | 139 (83) | ||
Unable to determine | 30 (10) | 17 (13) | 13 (8) | ||
Number of Covariates | 1 | 95 (39) | 42 (41) | 53 (38) | 0.5106 |
2 | 86 (36) | 32 (31) | 54 (39) | ||
3 | 40 (17) | 17 (17) | 23 (17) | ||
4 | 11 (5) | 5 (5) | 6 (4) | ||
5 or more | 9 (4) | 6 (6) | 3 (2) | ||
Baseline Test for Significant Differences | No | 167 (57) | 76 (59) | 91 (55) | 0.5564 |
Yes | 126 (43) | 53 (41) | 73 (45) | ||
Unadjusted or Adjusted Analyses | Unadjusted | 49 (16) | 27 (21) | 22 (13) | 0.0100 |
Adjusted | 87 (29) | 27 (21) | 60 (36) | ||
Both | 162 (54) | 77 (59) | 85 (51) | ||
Reason for Adjustment (if applicable) | Pre-specified | 226 (91) | 88 (85) | 138 (95) | 0.0778c |
Data driven - Lack of balance | 5 (2) | 3 (3) | 2 (1) | ||
Data driven - Potential confounding | 6 (2) | 4 (4) | 2 (1) | ||
Other | 4 (2) | 3 (3) | 1 (1) | ||
Unable to determine | 8 (3) | 6 (6) | 2 (1) |