| I |
Evidence obtained from at least one properly randomized trial |
| II-1 |
Evidence obtained from a well-designed controlled trial without randomization |
| II-2 |
Evidence obtained from well-designed cohort or case controlled analytic studies, preferably from more than one centre of research |
| II-3 |
Evidence obtained from comparisons between times and places, with or without the intervention. Dramatic results in uncontrolled experiments could also be included in this category |
| III |
Opinions of respected authorities, based on clinical experience, descriptive studies or reports of expert committees |
| Recommendations for preventive measures |
| A |
There is good evidence to support this recommendation |
| B |
There is fair evidence to support this recommendation |
| C |
There is poor evidence to support this recommendation, but a recommendation could be made on other grounds |
| D |
There is fair evidence to support the recommendation of exclusion |
| E |
There is good evidence to support the recommendation of exclusion |
