Table 1.
Overview of predefined moderator variables, frequency of effect sizes (n) and pooling of levels
| Variable | Level | n | Pooled level |
|---|---|---|---|
| Level of blinding | Single | 11 | |
| Double | 48 | ||
| Not reported | 18 | ||
| Experimental design | Between-subjects | 17 | |
| Between-subjects with baseline | 19 | ||
| Within-subjects | 22 | ||
| Mixed | 19 | ||
| Cognitive domain | Risk-based decision-making | 3 | a) |
| Executive functions | 8 | a) | |
| Inhibition | 8 | a) Executive functions | |
| Impulsivity | 14 | ||
| Language | 6 | ||
| Reward learning | 6 | ||
| Social cognition | 13 | b) | |
| Empathy | 4 | b) | |
| Theory of mind | 15 | b) Social cognition | |
| Target electrode placement | F3 | 22 | |
| F4 | 7 | a) | |
| F6 | 2 | a) | |
| FC6 | 4 | a) Right prefrontal | |
| FP2 | 3 | b) | |
| FZ | 20 | b) Central prefrontal | |
| P6 | 15 | ||
| T7* | 4 | ||
| Timing | Online | 33 | |
| Offline | 44 | ||
| Distance between target and return electrode | One* | 3 | |
| Two | 18 | ||
| Mixed | 19 | ||
| Other | 22 | ||
| Not reported | 15 | ||
| Measure | Reaction time | 38 | |
| Accuracy | 18 | ||
| Other | 21 | ||
| Pathology** | Aphasia | 2 | |
| None | 75 | ||
| Stimulation intensity (mA) | 1 | 30 | |
| 1.5 | 7 | ||
| 2 | 40 | ||
| Stimulation duration (min)** | 13 | 4 | |
| 20 | 73 |
Subgroups marked with *were excluded from subgroup analyses because of group size (k < 5), as they could not be reasonably pooled together with other subgroups
**The pre-defined moderator variables “pathology” and “stimulation duration” were excluded from subgroup analyses, as not enough data points were found for subgroups