Categories of research evidence applied to statements (adapted from Buckley et al)73
| Category | Methodology | Descriptor |
| A | Randomised, controlled trials (RCTs) | Data are overwhelmingly from RCT studies, and findings are consistent. |
| B | RCT (limited data) and high-quality observational data | Few RCTs exist; they have small sample sizes and/or results are inconsistent. AND/OR Observational studies supported by evidence of causality from laboratory-based or experimental studies. |
| C | Non-RCTs, observational studies | Outcomes are from uncontrolled, non-randomised and/or observational studies (overwhelmingly cross-sectional). |
| D | Expert consensus | Evidence is insufficient for categorisation in A–C; panel’s expert opinion. |