2. Risk of bias summary table.
| Area of potential bias | Number of studies (N = 35) | ||
| High risk | Unclear risk | Low risk | |
| Randomisation | 1 | 27 | 7 |
| Allocation bias | 0 | 34 | 1 |
| Blinding | 3 | 9 | 23 |
| Incomplete outcomes | 3 | 10 | 22 |
| Selective reporting | 6 | 5 | 24 |
| Other bias | 0 | 9 | 26 |
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