The STOX classification system
| Evidence type | STOX classification | Health Evidence Bulletins Wales classification33 | Description |
|---|---|---|---|
| Systematic reviews | S1 | I | Comprehensive systematic review containing at least one randomised controlled trial |
| S2 | IV | Comprehensive systematic review | |
| Trials | T1 | II | Randomised controlled trial |
| T2 | III | Non randomised controlled trial | |
| T3 | III | Before and after interventional trial | |
| Observational studies | O1 | IV | Cohort study |
| O2 | IV | Case-control study | |
| O3 | IV | Cross sectional/longitudinal study (including statistical data) | |
| O4 | IV | Study using qualitative methods only | |
| O5 | IV | Case study (for example, a single housing estate) | |
| EXpressions of opinion | X | V | Formal consensus or other professional opinion. (This category includes literature reviews where there is no indication of a systematic approach and models based on reviews of the literature) |