Grade A (Evidence Levels la, lb) Requires at least one randomised controlled trial as part of the body of literature of overall good quality and consistency addressing the specific recommendation     Grade b (Evidence Levels lla, llb) Requires availability of well conducted clinical studies but no randomised controlled trials on the topic of the recommendation     Grade c (Evidence Levels lV) Requires evidence from expert committee reports or opinions and/or clinical experience of respected authorities; indicates absence of directly applicable studies of good quality     la Meta analysis of randomised controlled trials     lb At least one randomised controlled trial     lla At least one well designed study without randomisation     llb At least one well designed quasi-experimental Study     lll Well designed non-experimental descriptive studies     lV Expert committee reports or opinions and/or clinical experience of respected authorities