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Lloyd- Smith hierarchy of evidence
| Level of evidence | Study design | Selected studies |
|---|---|---|
| Ia | Meta-analysis of RCT | 0 |
| Ib | One individual randomized controlled study | 4 |
| IIa | One well-designed, nonrandomized studies | 9 |
| IIb | Well-designed quesi-experimental study | 1 |
RCT=Randomized controlled trial
