Grading of evidence sources and recommendations
| Evidence or recommendation | Grade |
| Evidence source as recommended by the Agency for Health Care Policy Research (AHCPR): | |
| Meta-analysis of randomised controlled trials (RCT) | 1a |
| One or more RCT | 1b |
| One or more controlled trials (without randomisation) | 2a |
| Other well designed studies (quasiexperimental) | 2b |
| Non-experimental studies (descriptive studies such as comparative or correlation studies, or case-control studies) | 3 |
| Expert committee opinions, clinical experience | 4 |
| Preliminary recommendations for treatment of psoriatic arthritis (using the best available evidence extracted from published literature): | |
| Category 1 evidence | A |
| Category 2 evidence, or extrapolation from category 1 evidence | B |
| Category 3 evidence, or extrapolation from category 1 or 2 evidence | C |
| Category 4 evidence or extrapolation from category 2 or 3 evidence | D |