Appendix A: Grading scheme

Appendix A: Grading scheme

All evidence was classified according to an accepted hierarchy of evidence that was originally adapted from the US Agency for Healthcare Policy and Research Classification (see Box 1). Recommendations were then graded A to C based on the level of associated evidence. This grading scheme is based on a scheme formulated by the Clinical Outcomes Group of the NHS Executive (1996).

Box 1: Hierarchy of evidence and recommendations grading scheme


Type of evidence




Evidence obtained from a single randomised controlled trial or a meta‑analysis of randomised controlled trials


At least one randomised controlled trial as part of a body of literature of overall good quality and consistency addressing the specific recommendation (evidence level I) without extrapolation


Evidence obtained from at least one well‑designed controlled study without randomisation


Well‑conducted clinical studies but no randomised clinical trials on the topic of recommendation (evidence levels II or III); or extrapolated from level I evidence


Evidence obtained from at least one other well‑designed quasi‑experimental study


Evidence obtained from well‑designed non‑experimental descriptive studies, such as comparative studies, correlation studies and case studies


Evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities


Expert committee reports or opinions and/or clinical experiences of respected authorities (evidence level IV) or extrapolated from level I or II evidence. This grading indicates that directly applicable clinical studies of good quality are absent or not readily available


Recommended good practice based on the clinical experience of the GDG.

Adapted from Eccles M, Mason J (2001) How to develop cost‑conscious guidelines. Health Technology Assessment 5:16 and Mann T (1996) Clinical Guidelines: Using Clinical Guidelines to Improve Patient Care Within the NHS. London: Department of Health.