Grading criteria for studies
| *Modified from Clinical Guidance Outcomes Group.20 |
| Grade I (strong evidence) |
| RCTs or review of RCTs |
| • IA Calculation of sample size and accurate and standard definition of appropriate outcome variables |
| • IB Accurate and standard definition of appropriate outcome variables |
| • IC Neither of the above |
| Grade II (fairly strong evidence) |
| Prospective study with a comparison group (non-randomised controlled trial, good observational study or retrospective study that controls effectively for confounding variables). |
| • IIA Calculation of sample size and accurate, standard definition of appropriate outcome variables and adjustment for the effects of important confounding variables. |
| • IIB One or more of the above |
| Grade III (weaker evidence) |
| Retrospective or observational studies |
| • IIIA Comparison group, calculation of sample size, accurate and standard definition of appropriate outcome variables. |
| • IIIB Two or more of the above |
| • IIIC One or none of the above* |
| Grade IV (weak evidence) |
| Cross sectional study, Delphi exercise, consensus of experts |