Level of evidence base for clinical management recommendations: number by level of evidence as defined by US Agency for Health Care Policy and Research
| Level A | Level B | Level C | |
| TS | 0 | 6 | 16 |
| Marfan syndrome | 2 | 14 | 11 |
| MD | 0 | 2 | 19 |
| NF1 | 0 | 14 | 20 |
| HD | 0 | 3 | 15 |
| Total | 2 (2%) | 39 (32%) | 81 (66%) |
Level A requires at least one RCT as part of a body of publications of overall good quality and consistency addressing specific recommendation (evidence levels 1a, 1b).
Level B requires the availability of well conducted clinical studies but no RCT on the topic of the recommendation (evidence levels 2a, 2b, 3).
Level C requires evidence obtained from expert committee reports or opinions/clinical experiences of respected authorities. Indicates an absence of directly applicable studies of good quality.