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1. Evidence obtained from at least one well-designed and conducted randomized controlled trial

2. Evidence obtained from well-designed and conducted nonrandomized controlled trials

3. Evidence obtained from well-designed and conducted cohort or case-control studies, preferably from more than one center or research group

4. Evidence obtained from multiple-time series with or without intervention

5. Opinions of respected authorities based on clinical experience, descriptive studies, or reports of expert committees

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