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 |