Table 2 Grading system

Grading of recommendations

A

Supported by at least two level I investigations

B

Supported by one level I investigation

C

Supported by level II investigations only

D

Supported by at least one level III investigation

E

Supported by level IV or V evidence

Grading of evidence

I

Evidence is based on randomised controlled trials (or meta-analysis of such trials) of adequate size to ensure a low risk of incorporating false-positive (alpha) or false-negative (beta) results

II

Evidence is based on randomised controlled trials that are too small to provide 'level I' evidence. They may show either positive trends that are not statistically significant or no trends and are associated with a high risk of false-negative results

III

Evidence is based on non-randomised controlled or cohort studies, case series, case-control studies or cross-sectional studies

IV

Evidence is based on non-randomised, historical controls and expert opinion

V

Evidence is based on case series, uncontrolled studies, and expert opinion