| Category | n | References | |
|---|---|---|---|
| 1 | Direct comparison | 6 | [53, 104, 119, 121, 124, 127] |
| 2 | Indirect comparison | 7 | [122, 123, 126, 128, 138, 139, 149] |
| 3 | Interaction/moderation | 7 | [125, 130, 131, 137, 146,147,148] |
| 4 | Modeling/stratification | 3 | [140, 151, 152] |
| 5 | Combination | 12 | [40, 82, 120, 129, 132,133,134, 136, 143,144,145, 153] |