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Quantity and quality of research articles according to Oxford Centre for Evidence-Based Medicine 2011 Levels of Evidence as used in this review.
| Level | Levels of Evidence | Quantity of Articles |
|---|---|---|
| 1 | Systematic review of randomized trials or n-of-1 trials | 0 |
| 2 | Randomized trial or observational study with dramatic effect | 9 |
| 3 | Non-randomized controlled cohort/follow-up study | 16 |
| 4 | Case-series, case-control studies, or historically controlled studies | 0 |
| 5 | Mechanism based reasoning | 0 |
