Users' guides to the medical literature. IX. A method for grading health care recommendations. Evidence-Based Medicine Working Group. - Guyatt GH; Sackett DL; Sinclair JC; Hayward R; Cook D; Cook RJ; Guyatt, G H; Sackett, D L; Sinclair, J C; Hayward, R; Cook, D J; Cook, R J (JAMA: Journal of the American Medical Association, 1995)