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Table 2 Summary of assessment of bias

From: A scoping review of the problems and solutions associated with contamination in trials of complex interventions in mental health

Variable Level Trials with individual-level randomisation (n) Trials with cluster randomisation (n)
Jadad score (possible range of 0–5; higher scores indicate lower likelihood of bias) 0 2 (1.4%) 1 (1.1%)
1 26 (18.8%) 22 (23.9%)
2 44 (31.9%) 32 (34.8%)
3 66 (47.8%) 37 (40.2%)
Allocation sequence adequately generated Low risk 75 (53.2%) 44 (47.3%)
High risk 3 (2.1%) 1 (1.1%)
Unclear 63 (44.7%) 48 (51.6%)
Allocation sequence adequately concealed Low risk 30 (21.3%) 18 (19.3%)
High risk 3 (2.1%) 1 (1.1%)
Unclear 108 (76.6%) 74 (79.6%)
Randomisation after consent obtained Low risk 116 (82.3%) 23 (24.7%)
High risk 6 (4.3%) 39 (41.9%)
Unclear / NA 19 (13.5%) 31 (33.3%)
Randomisation after baseline measures were completed Low risk 56 (39.7%) 15 (16.1%)
High risk 14 (9.9%) 41 (44.1%)
Unclear 71 (50.4) 37 (39.8%)
Baseline outcome measurements similar across trial arms Low risk 109 (77.3%) 70 (75.3%)
High risk 9 (6.4%) 11 (11.8%)
Unclear / NA 23 (16.3%) 12 (12.9%)
Baseline demographic characteristics similar across trial arms Low risk 121 (85.8%) 69 (74.2%)
High risk 3 (2.1%) 18 (19.4%)
Unclear / NA 17 (12.1%) 6 (6.5%)
Knowledge of allocation adequately concealed Low risk 0 (0%) 0 (0%)
High risk 141 (100%) 93 (100%)
Blinded outcome assessment Low risk 63 (44.7%) 29 (31.2%)
High risk 8 (5.7%) 17 (18.3%)
Unclear / NA 70 (49.6%) 47 (50.5%)
Incomplete outcome data Low risk 35 (24.8%) 22 (23.7%)
High risk 82 (58.2%) 57 (61.3)
Unclear / NA 24 (17.0%) 14 (15.1%)
Similar attrition between trial arms Low risk 85 (60.3%) 51 (54.8%)
High risk 30 (21.3%) 25 (26.9%)
Unclear / NA 26 (18.4%) 17 (18.3%)