| Levels of Evidence |
| Papers have been assessed as to the levels of evidence that they support as follows: |
| Level 1 |
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Based on randomised, controlled trials (or meta-analysis of such trials) of adequate size to ensure a low risk of incorporating false-positive or false-negative results |
| Level 2 |
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Based on randomised, controlled trials that are too small to provide level 1 evidence. These may show either positive trends that are not statistically significant or no trends which are associated with a high risk of false-negative results |
| Level 3 |
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Based on non-randomised, controlled or cohort studies, case series, case-controlled studies or cross-sectional surveys |
| Level 4 |
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Based on the opinion of respected authorities or that of expert committees as indicated in published consensus conferences or guidelines |
| Level 5 |
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Based on the opinion of those individuals who have written and reviewed these guidelines, based on their experience, knowledge of the relevant literature and discussion with their peers |