Table 1.
Characteristics of the cluster trials included in this review
| Characteristics | Included trials (123 cluster trials) |
|---|---|
| Type of intervention, n (%) | |
| Healthcare practice | 63 (51.2) |
| Lifestyle changes | 25 (20.3) |
| Educational | 27 (22.0) |
| New drug | 5 (4.1) |
| Vaccination/screening | 3 (2.4) |
| Type of control intervention, n (%) | |
| Standard practice | 94 (76.4) |
| Active control | 27 (22.0) |
| Placebo | 2 (1.6) |
| Primary outcome, n (%) | |
| Continuous | 65 (52.8) |
| Binary | 57 (46.4) |
| Categorical | 1 (0.8) |
| Investigation of adverse events, n (%) | 12 (9.8) |
| Number of trial arms, n (%) | |
| 2 | 106 (86.2) |
| 3-4 | 17 (13.8) |
| Level of intervention, n (%) | |
| Cluster level | 65 (52.8) |
| Individual level | 58 (47.2) |
| Unit of analysis, n (%) | |
| Clusters | 6 (4.9) |
| Individuals | 117 (95.1) |
| Length of intervention, n (%) | |
| One-off | 5 (4.1) |
| Short term | 35 (28.4) |
| Long term | 83 (67.5) |
| Clusters randomised per arm, Median (1st-3rd quartiles) | 12 (7-24) |
| Range | 2-199 |
| Cluster size, Median (1st-3rd quartiles)a | 27 (10-65) |
| Rangea | 2-14350 |
| Primary analysis population, n (%) | |
| Intention-to-treat | 119 (96.8) |
| Per protocol/as treated | 4 (3.2) |
a
Based on the average number of individuals per cluster reported in each trials.