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The therapeutic hierarchy32
| Single large randomized controlled trial |
| Systematic review of several small randomized controlled trials |
| Single small randomized controlled trial |
| Systematic review of several cohort studies |
| Single cohort study |
| Systematic review of several case-control studies |
| Single case-control study |
| Systematic review of several cross-sectional studies |
| Single cross-sectional study |
| Case series |
