Quality of evidence (QoE) levels and source of evidence
| QoE | Definition |
| I | Evidence from at least one properly designed randomised, controlled trial; with the primary objective of the study aligned with the recommendation being made. |
| II | Evidence from at least one well-designed clinical trial, without randomisation; from cohort or case-controlled analytic studies (preferably from more than one centre); from multiple time series; or from dramatic results of uncontrolled experiments. |
| r | Meta-analysis or systematic review of randomised control trial |
| t | Transferred evidence i.e. results from different patient cohorts, or similar immune-status situation |
| h | Comparator group: historical control |
| u | Uncontrolled trials |
| a | Published abstract presented at an international symposium or meeting |
| III | Evidence from opinions of respected authorities, based on clinical experience, descriptive case studies, or reports of expert committees. |