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Reasons recorded for persistent uncertainty
| Available evidence supporting uncertainty | |
| A | No systematic review available. |
| B | Systematic review available, but authors did not find any randomised controlled trials in the literature. |
| C | Systematic review available, some randomised controlled trials found, but no formal meta-analysis performed. |
| D | Systematic review with meta-analysis available, uncertainty persists. |
| E | Cochrane systematic review with meta-analysis performed, results inclusive. |
