| Level . | Therapy . |
|---|---|
1a | Systematic review of similar RCTs |
1b | Single RCT of good quality |
1c | All or none (e.g. all treated patients cured/died) |
2a | Systematic review of similar cohort studies |
2b | Single cohort study |
2c | ‘Outcomes’ research; ecological studies |
3a | Systematic review of similar case-control studies |
3b | Single case–control study |
4 | Case-series, poor quality cohort, and case–control studies |
5 | Expert opinion or based on physiology or lab research |
| Level . | Therapy . |
|---|---|
1a | Systematic review of similar RCTs |
1b | Single RCT of good quality |
1c | All or none (e.g. all treated patients cured/died) |
2a | Systematic review of similar cohort studies |
2b | Single cohort study |
2c | ‘Outcomes’ research; ecological studies |
3a | Systematic review of similar case-control studies |
3b | Single case–control study |
4 | Case-series, poor quality cohort, and case–control studies |
5 | Expert opinion or based on physiology or lab research |
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