Table 1.
General characteristics of included studies
| Characteristics | Overall (n=1122) (No, col %) | Not registered (n=529) (No, row %) | Registered (n=593) (No, row %) | P value | Prospectively registered (n=220) (No, row %)* | Retrospectively registered (n=373) (No, row %)* | P value† |
|---|---|---|---|---|---|---|---|
| Study centres: | |||||||
| Single | 300 (26.7) | 157 (52.3) | 143 (47.7) | <0.001 | 43 (14.3) | 100 (33.3) | <0.001 |
| Multiple | 298 (26.6) | 65 (21.8) | 233 (78.2) | 111 (37.3) | 122 (40.9) | ||
| Unclear | 524 (46.7) | 307 (58.6) | 217 (41.4) | 66 (12.6) | 151 (28.8) | ||
| Design: | |||||||
| Parallel group | 953 (84.9) | 442 (46.4) | 511 (53.6) | 0.24 | 188 (19.7) | 323 (33.9) | 0.36 |
| Cluster | 31 (2.8) | 14 (45.2) | 17 (54.8) | 4 (12.9) | 13 (41.9) | ||
| Crossover | 98 (8.7) | 48 (49.0) | 50 (51.0) | 22 (22.5) | 28 (28.6) | ||
| Other | 40 (3.6) | 25 (62.5) | 15 (37.5) | 6 (15.0) | 9 (22.5) | ||
| No of arms: | |||||||
| 2 | 892 (79.5) | 424 (47.5) | 468 (52.5) | 0.03 | 170 (19.1) | 298 (33.4) | 0.08 |
| 3 | 146 (13.0) | 65 (44.5) | 81 (55.5) | 35 (24.0) | 46 (31.5) | ||
| 4 | 61 (5.4) | 35 (57.4) | 26 (42.6) | 10 (16.4) | 16 (26.2) | ||
| >4 | 23 (2.1) | 5 (21.7) | 18 (78.3) | 5 (21.7) | 13 (56.5) | ||
| Median (interquartile range) sample size (No of randomised participants) | 86 (43-193) | 66 (39-144) | 105 (51-254) | <0.001 | 117 (59-296) | 100 (48-232) | <0.001 |
| Funding: | |||||||
| Non-industry | 513 (45.7) | 249 (48.5) | 264 (51.5) | <0.001 | 79 (15.4) | 185 (36.1) | <0.001 |
| Solely or partly industry | 302 (26.9) | 65 (21.5) | 237 (78.5) | 117 (38.7) | 120 (39.7) | ||
| Unclear | 307 (27.4) | 215 (70.0) | 92 (30.0) | 24 (7.8) | 67 (22.2) | ||
| Journal specific variables | |||||||
| Median (interquartile range) impact factor | 3 (2-5) | 2 (1-3) | 4 (2-6) | <0.001 | 5 (3-8) | 3 (2-5) | <0.001 |
| General medical journals*: | |||||||
| Yes | 34 (3.0) | 1 (3.0) | 33 (97.1) | <0.001 | 21 (61.8) | 12 (35.3) | <0.001 |
| No | 1088 (97.0) | 528 (48.5) | 560 (51.5) | 199 (18.3) | 361 (33.2) | ||
| ICMJE endorsed: | |||||||
| Yes | 268 (23.9) | 84 (31.3) | 184 (68.7) | <0.001 | 81 (30.2) | 103 (38.4) | <0.001 |
| No | 854 (76.1) | 445 (52.1) | 409 (47.9) | 139 (16.3) | 270 (31.6) | ||
ICMJE=International Committee of Medical Journal Editors.
*
Percentages obtained from 3×2 table including trials prospectively registered, retrospectively registered, and not registered.
†
Generated from χ2 test comparing proportion of trials prospectively registered, retrospectively registered, and not registered.