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Table 2 Supporting comments for judgment of risk of bias regarding randomisation

From: Risk of bias judgments for random sequence generation in Cochrane systematic reviews were frequently not in line with Cochrane Handbook

Categories of supporting comments for judgments of bias associated with the generation of randomisation sequence Total, N (%) High, N (%) Unclear, N (%) Low, N (%)
Random number table (low risk†) 883 (8.7) 11 (1.2) 31 (3.5) 841 (95.2)
 Random number table 883 (100.0) 11 (1.2) 31 (3.5) 841 (95.2)
Randomisation via computer/software/internet (low risk†) 2850 (28.2) 2 (0.1) 36 (1.3) 2812 (98.7)
 Computer/software generated 2459 (86.3) 0 (0.0) 17 (0.7) 2442 (99.3)
 IVRS* 60 (2.1) 0 (0.0) 7 (11.7) 53 (88.3)
 Minimisation 103 (3.6) 2 (1.9) 8 (7.8) 93 (90.3)
 Random number generator (without mention of computer) 98 (3.4) 0 (0.0) 0 (0.0) 98 (100.0)
 Web based 130 (4.6) 0 (0.0) 4 (3.1) 126 (96.9)
Mechanical method of randomisation (low risk†) 359 (3.6) 7 (1.9) 37 (10.3) 315 (87.7)
 Coin tossing 85 (23.7) 0 (0.0) 1 (1.2) 84 (98.8)
 Drawing of lots 201 (56.0) 4 (2.0) 12 (6.0) 185 (92.0)
 Shuffling cards or envelopes 60 (16.7) 3 (5.0) 24 (40.0) 33 (55.0)
 Throwing dice 13 (3.6) 0 (0.0) 0 (0.0) 13 (100.0)
Incomplete or inappropriate randomisation (high risk†) 305 (3.0) 264 (86.6) 32 (10.5) 9 (3.0)
 Quasi random 238 (78.0) 209 (87.8) 22 (9.2) 7 (2.9)
 Incomplete, erroneous randomisation 41 (13.4) 34 (82.9) 7 (17.1) 0 (0.0)
 Judgment, preference, availability 26 (8.5) 21 (80.8) 3 (11.5) 2 (7.7)
Method of randomisation was not described (unclear risk†) 5706 (56.5) 81 (1.4) 4651 (81.5) 974 (17.1)
 Not described 4586 (80.4) 69 (1.5) 4272 (93.2) 245 (5.3)
 Block randomisation/stratification 679 (11.9) 2 (0.3) 219 (32.3) 458 (67.5)
 Envelopes 247 (4.3) 3 (1.2) 117 (47.4) 127 (51.4)
 Central randomisation (statistics department, pharmacy, third party) 124 (2.2) 1 (0.8) 0 (0.0) 123 (99.2)
 Baseline imbalance between groups 41 (0.7) 6 (14.6) 35 (85.4) 0 (0.0)
 Baseline balance between groups 29 (0.5) 0 (0.0) 8 (27.6) 21 (72.4)
Total, N (%) 10103 (100.0) 365 (3.6) 4787 (47.4) 4951 (49.0)
  1. *IVRS = Interactive Voice Response System. †Category RoB judgment according to Cochrane Handbook