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| Studies | References | No. of studies |
| Comparative studies | 11-18, 21, 24, 25, 27, 28, 33, 36, 37, 39, 41–46, 48 | 24 |
| Descriptive studies | 19, 20, 22, 23, 29, 30, 32, 34, 35, 38, 47 | 11 |
| Prospective studies | 11-18, 21, 24, 25, 33, 36, 39, 41–46, 48 | 21 |
