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Table 1 Characteristics of articles of parallel group randomized trials by year of publication

From: Reporting on covariate adjustment in randomised controlled trials before and after revision of the 2001 CONSORT statement: a literature review

Year of Publication 2000
(n = 355)
2006
(n = 421)
% difference
(95% CI)
P-value
Outcome specification     
   Primary 180 (50.7%) 273 (64.9%) 14.1 (7.2 to 21.0) <0.0001
   Unspecified 175 (49.3%) 148 (35.1%)   
Centre involved*     
   Multiple centres 119 (34.1%) 138 (33.7%) -0.4 (-7.2 to 6.3) 0.9
   Single centre 230 (65.9%) 272 (66.3%)   
Number of intervention groups 261 (73.5%) 328 (77.9%)   0.2
   2 57 (16.1%) 64 (15.2%)   
   3 37 (10.4%) 29 (6.9%)   
   > 3     
Performed stratified randomisation 56 (15.8%) 85 (20.2%) 4.4 (-1.0 to 9.8) 0.1
Sample size     
   < 50 116 (32.7%) 129 (30.6%)   
   51 - 150 141 (39.7%) 169 (39.9%)   
   151 - 300 49 (13.8%) 52 (12.4%)   
   301 - 450 20 (5.6%) 27 (6.6%)   
   > 450 29 (8.2%) 44 (10.5%)   
   Median (10th to 90th percentile) 91 (27 to 394) 80 (28 to 462)   0.7
Journal type     
   General medical 31 (8.7%) 36 (8.6%) -0.1 (3.8 to -4.2) 0.9
   Specialty 324 (91.3%) 385 (91.4%)   
Number of outcomes per trial     
   Median (range) 15 (1, 131) 14 (1, 372)   0.2
Type of outcomes (n = 7132) (n = 8299)   <0.0001
   Continuous 4984 (69.9%) 5705 (68.7%)   
   Binary 1961 (27.5%) 2357 (28.4%)   
   Time-to-event 47 (0.6%) 128 (1.5%)   
   Ordinal 140 (2.0%) 98 (1.2%)   
   Categorical 0 11 (0.1%)   
Adjusted analysis 84 (23.7%) 113 (26.8%) 3.1 (-2.9 to 9.3) 0.3
  1. * Unclear: 6 for year 2000 and 11 for year 2006
  2. Percentage difference = percentage in 2006 - percentage in 2000