Skip Navigation U.S. Department of Health and Human Services
Agency for Healthcare Research Quality
Archive print banner

Systems to Rate the Strength of Scientific Evidence

This information is for reference purposes only. It was current when produced and may now be outdated. Archive material is no longer maintained, and some links may not work. Persons with disabilities having difficulty accessing this information should contact us at: Let us know the nature of the problem, the Web address of what you want, and your contact information.

Please go to for current information.

Summary (continued)


The authors summarized more than 100 sources of information on systems for assessing study quality and strength of evidence for systematic reviews and technology assessments. After applying evaluative criteria based on key domains to these systems, they identified 19 study quality and seven strength of evidence grading systems that those conducting systematic reviews and technology assessment can use as starting points. In making this information available to the Congress and then disseminating it more widely, AHRQ can meet the congressional expectations set forth in the Healthcare Research and Quality Act of 1999 and outlined at the outset of the report. The broader agenda to be met is for those producing systematic reviews and technology assessments to apply these rating and grading schemes in ways that can be made transparent for groups developing clinical practice guidelines and other health-related policy advice. The authors have also offered a rich agenda for future research in this area, noting that the Congress can enable pursuit of this body of research through AHRQ and its EPC program. They are confident that the work and recommendations contained in this report will move the evidence-based practice field ahead in ways that will bring benefit to the entire health care system and the people it serves.

Return to Contents


1. Lohr KN, Carey TS. Assessing 'best evidence': issues in grading the quality of studies for systematic reviews. Joint Commission J Qual Improvement 1999;25:470-479.
2. Juni P, Witschi A, Bloch R, Egger M. The hazards of scoring the quality of clinical trials for meta-analysis. JAMA 1999;282:1054-1060.
3. Barnes DE, Bero LA. Why review articles on the health effects of passive smoking reach different conclusions. JAMA 1998;279:1566-1570.
4. Oxman AD, Guyatt GH. Validation of an index of the quality of review articles. J Clin Epidemiol 1991;44:1271-1278.
5. Oxman AD, Guyatt GH, Singer J, et al. Agreement among reviewers of review articles. J Clin Epidemiol 1991;44:91-98.
6. Irwig L, Tosteson AN, Gatsonis C, et al. Guidelines for meta-analyses evaluating diagnostic tests. Ann Intern Med 1994 Apr 15;120:667-676.
7. Sacks HS, Reitman D, Pagano D, Kupelnick B. Meta-analysis: an update. Mt Sinai J Med 1996;63:216-224.
8. Auperin A, Pignon JP, Poynard T. Review article: critical review of meta-analyses of randomized clinical trials in hepatogastroenterology. Alimentary Pharmacol Ther 1997;11:215-225.
9. Beck CT. Use of meta-analysis as a teaching strategy in nursing research courses. J Nurs Educ 1997;36:87-90.
10. Smith AF. An analysis of review articles published in four anaesthesia journals. Can J Anaesth 1997;44:405-409.
11. Clarke M., Oxman AD. Cochrane Reviewer's Handbook 4.0. The Cochrane Collaboration; 1999.
12. Khan KS, Ter Riet G, Glanville J, Sowden AJ, Kleijnen J. Undertaking Systematic Reviews of Research on Effectiveness. CRD's Guidance for Carrying Out or Commissioning Reviews: York, England: University of York, NHS Centre for Reviews and Dissemination; 2000.
13. New Zealand Guidelines Group. Tools for Guideline Development & Evaluation. Accessed July 10, 2000. Web Page. Available at:
14. Harbour R, Miller J. A new system [Scottish Intercollegiate Guidelines Network (SIGN)] for grading recommendations in evidence based guidelines. BMJ 2001;323:334-336.
15. Oxman AD, Cook DJ, Guyatt GH. Users' guides to the medical literature. VI. How to use an overview. Evidence-Based Medicine Working Group. JAMA 1994;272:1367-1371.
16. Cook DJ, Sackett DL, Spitzer WO. Methodologic guidelines for systematic reviews of randomized control trials in health care from the Potsdam Consultation on Meta-Analysis. J Clin Epidemiol 1995;48:167-171.
17. Cranney A, Tugwell P, Shea B, Wells G. Implications of OMERACT outcomes in arthritis and osteoporosis for Cochrane metaanalysis. J Rheumatol 1997;24:1206-1207.
18. de Vet HCW, de Bie RA, van der Heijden GJMG, Verhagen AP, Sijpkes P, Kipschild PG. Systematic reviews on the basis of methodological criteria. Physiotherapy June 1997;83(6):284-289.
19. Pogue J, Yusuf S. Overcoming the limitations of current meta-analysis of randomised controlled trials. Lancet 1998;351:47-52.
20. Sutton AJ, Abrams KR, Jones DR, Sheldon TA, Song F. Systematic reviews of trials and other studies. Health Technol Assess 1998;2:1-276.
21. Moher D, Cook DJ, Eastwood S, Olkin I, Rennie D, Stroup DF. Improving the quality of reports of meta-analyses of randomised controlled trials: the QUOROM statement. Quality of Reporting of Meta-analyses. Lancet 1999;354:1896-1900.
22. National Health and Medical Research Council (NHMRC). How to Use the Evidence: Assessment and Application of Scientific Evidence. Canberra, Australia: NHMRC; 2000.
23. Stroup DF, Berlin JA, Morton SC, et al. Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group. JAMA 2000;283:2008-2012.
24. Chalmers TC, Smith H Jr, Blackburn B, et al. A method for assessing the quality of a randomized control trial. Control Clin Trials 1981;2:31-49.
25. Evans M, Pollock AV. A score system for evaluating random control clinical trials of prophylaxis of abdominal surgical wound infection. Br J Surg 1985;72:256-260.
26. Liberati A, Himel HN, Chalmers TC. A quality assessment of randomized control trials of primary treatment of breast cancer. J Clin Oncol 1986;4:942-951.
27. Colditz GA, Miller JN, Mosteller F. How study design affects outcomes in comparisons of therapy. I: Medical. Stat Med 1989;8:441-454.
28. Gotzsche PC. Methodology and overt and hidden bias in reports of 196 double-blind trials of nonsteroidal antiinflammatory drugs in rheumatoid arthritis. Control Clin Trials 1989;10:31-56.
29. Kleijnen J, Knipschild P, ter Riet G. Clinical trials of homoeopathy. BMJ 1991;302:316-323.
30. Detsky AS, Naylor CD, O'Rourke K, McGeer AJ, L'Abbe KA. Incorporating variations in the quality of individual randomized trials into meta-analysis. J Clin Epidemiol 1992;45:255-265.
31. Cho MK, Bero LA. Instruments for assessing the quality of drug studies published in the medical literature. JAMA 1994;272:101-104.
32. Goodman SN, Berlin J, Fletcher SW, Fletcher RH. Manuscript quality before and after peer review and editing at Annals of Internal Medicine. Ann Intern Med 1994;121:11-21.
33. Fahey T, Hyde C, Milne R, Thorogood M. The type and quality of randomized controlled trials (RCTs) published in UK public health journals. J Public Health Med 1995;17:469-474.
34. Jadad AR, Moore RA, Carroll D, et al. Assessing the quality of reports of randomized clinical trials: is blinding necessary? Control Clin Trials 1996;17:1-12.
35. Khan KS, Daya S, Collins JA, Walter SD. Empirical evidence of bias in infertility research: overestimation of treatment effect in crossover trials using pregnancy as the outcome measure. Fertil Steril 1996;65:939-945.
36. van der Heijden GJ, van der Windt DA, Kleijnen J, Koes BW, Bouter LM. Steroid injections for shoulder disorders: a systematic review of randomized clinical trials. Brit J Gen Pract 1996;46:309-316.
37. Bender JS, Halpern SH, Thangaroopan M, Jadad AR, Ohlsson A. Quality and retrieval of obstetrical anaesthesia randomized controlled trials. Can J Anaesth 1997;44:14-18.
38. Sindhu F, Carpenter L, Seers K. Development of a tool to rate the quality assessment of randomized controlled trials using a Delphi technique. J Adv Nurs 1997;25:1262-1268.
39. van Tulder MW, Koes BW, Bouter LM. Conservative treatment of acute and chronic nonspecific low back pain. A systematic review of randomized controlled trials of the most common interventions. Spine 1997;22:2128-2156.
40. Downs SH, Black N. The feasibility of creating a checklist for the assessment of the methodological quality both of randomised and non-randomised studies of health care interventions. J Epidemiol Community Health 1998;52:377-384.
41. Moher D, Pham B, Jones A, et al. Does quality of reports of randomised trials affect estimates of intervention efficacy reported in meta-analyses? Lancet 1998;352:609-613.
42. Turlik MA, Kushner D. Levels of evidence of articles in podiatric medical journals. J Am Podiatr Med Assoc 2000;90:300-302.
43. DerSimonian R, Charette LJ, McPeek B, Mosteller F. Reporting on methods in clinical trials. N Engl J Med 1982;306:1332-1337.
44. Poynard T, Naveau S, Chaput JC. Methodological quality of randomized clinical trials in treatment of portal hypertension. In Methodology and Reviews of Clinical Trials in Portal Hypertension. Excerpta Medica; 1987:306-311.
45. Reisch JS, Tyson JE, Mize SG. Aid to the evaluation of therapeutic studies. Pediatrics 1989;84:815-827.
46. Imperiale TF, McCullough AJ. Do corticosteroids reduce mortality from alcoholic hepatitis? A meta-analysis of the randomized trials. Ann Intern Med 1990;113:299-307.
47. Spitzer WO, Lawrence V, Dales R, et al. Links between passive smoking and disease: a best-evidence synthesis. A report of the Working Group on Passive Smoking. Clin Invest Med 1990;13:17-42; discussion 43-46.
48. Verhagen AP, de Vet HC, de Bie RA, et al. The Delphi list: a criteria list for quality assessment of randomized clinical trials for conducting systematic reviews developed by Delphi consensus. J Clin Epidemiol 1998;51:1235-1241.
49. National Health and Medical Research Council (NHMRC). How to Review the Evidence: Systematic Identification and Review of the Scientific Literature. Canberra, Australia: NHMRC; 2000.
50. Zaza S, Wright-De Aguero LK, Briss PA, et al. Data collection instrument and procedure for systematic reviews in the Guide to Community Preventive Services. Task Force on Community Preventive Services. Am J Prev Med 2000;18:44-74.
51. Schulz KF, Chalmers I, Hayes RJ, Altman DG. Empirical evidence of bias. Dimensions of methodological quality associated with estimates of treatment effects in controlled trials. JAMA 1995;273:408-412.
52. Prendiville W, Elbourne D, Chalmers I. The effects of routine oxytocic administration in the management of the third stage of labour: an overview of the evidence from controlled trials. Br J Obstet Gynaecol 1988;95:3-16.
53. Guyatt GH, Sackett DL, Cook DJ. Users' guides to the medical literature. II. How to use an article about therapy or prevention. B. What were the results and will they help me in caring for my patients? Evidence-Based Medicine Working Group. JAMA 1994;271:59-63.
54. Guyatt GH, Sackett DL, Cook DJ. Users' guides to the medical literature. II. How to use an article about therapy or prevention. A. Are the results of the study valid? Evidence-Based Medicine Working Group. JAMA 1993;270:2598-2601.
55. The Standards of Reporting Trials Group. A proposal for structured reporting of randomized controlled trials. JAMA 1994;272:1926-1931.
56. The Asilomar Working Group on Recommendations for Reporting of Clinical Trials in the Biomedical Literature. Checklist of information for inclusion in reports of clinical trials. Ann Intern Med 1996;124:741-743.
57. Moher D, Schulz KF, Altman DG, for the CONSORT Group. The CONSORT statement: revised recommendations for improving the quality of reports of parallel-group randomised trials. JAMA 2001;285:1987-1991.
58. Aronson N, Seidenfeld J, Samson DJ, et al. Relative Effectiveness and Cost-Effectiveness of Methods of Androgen Suppression in the Treatment of Advanced Prostate Cancer. Evidence Report/Technology Assessment No. 4. Rockville, MD.: Agency for Health Care Policy and Research. AHCPR Publication No.99-E0012; 1999.
59. Lau J, Ioannidis J, Balk E, et al. Evaluating Technologies for Identifying Acute Cardiac Ischemia in Emergency Departments. Evidence Report/Technology Assessment: No. 26. Rockville, MD.: Agency for Healthcare Research and Quality. AHRQ Publication No. 01-E006 (Contract 290-97-0019 to the New England Medical Center); 2000.
60. Chestnut RM, Carney N, Maynard H, Patterson P, Mann NC, Helfand M. Rehabilitation for Traumatic Brain Injury. Evidence Report/Technology Assessment No. 2. Rockville, MD.: Agency for Health Care Policy and Research. AHCPR Publication No. 99-E006; 1999.
61. Jadad AR, Boyle M, Cunningham C, Kim M, Schachar R. Treatment of Attention-Deficit/Hyperactivity Disorder. Evidence Report/Technology Assessment No. 11. Rockville, MD.: Agency for Healthcare Research and Quality. AHRQ Publication No. 00-E005; 1999.
62. Heidenreich PA, McDonald KM, Hastie T, et al. An Evaluation of Beta-Blockers, Calcium Antagonists, Nitrates, and Alternative Therapies for Stable Angina. Evidence Report/Technology Assessment No. 10. Rockville, MD: Agency for Healthcare Research and Quality. AHRQ Publication No. 00-E003; 1999.
63. Mulrow CD, Williams JW, Trivedi M, Chiquette E, Aguilar C, Cornell JE. Treatment of Depression: Newer Pharmacotherapies. Evidence Report/Technology Assessment No. 7. Rockville, MD.: Agency for Healthcare Research and Quality. AHRQ Publication No. 00-E003; 1999.
64. Vickrey BG, Shekelle P, Morton S, Clark K, Pathak M, Kamberg C. Prevention and Management of Urinary Tract Infections in Paralyzed Persons. Evidence Report/Technology Assessment No. 6. Rockville, MD.: Agency for Health Care Policy and Research. AHCPR Publication No. 99-E008; 1999.
65. West SL, Garbutt JC, Carey TS, et al. Pharmacotherapy for Alcohol Dependence. Evidence Report/Technology Assessment No. 3. Rockville, MD.: Agency for Health Care Policy and Research. AHCPR Publication No. 99-E004; 1999.
66. McNamara RL, Miller MR, Segal JB, et al. Management of New Onset Atrial Fibrillation. Evidence Report/Technology Assessement No.12. Rockville, MD.: Agency for Healthcare Research and Quality; AHRQ Publication No. 01-E026; 2001.
67. Ross S, Eston R, Chopra S, French J. Management of Newly Diagnosed Patients With Epilepsy: A Systematic Review of the Literature. Evidence Report/Technology Assessment No. 39; Rockville, Md: Agency for Healthcare Research and Quality. AHRQ Publication No. 01-E029; 2001.
68. Goudas L, Carr DB, Bloch R, et al. Management of Cancer Pain. Evidence Report/Technology Assessment. No. 35 (Contract 290-97-0019 to the New England Medical Center). Rockville, MD.: Agency for Health Care Policy and Research. AHCPR Publication No. 99-E004; 2000.
69. Corrao G, Bagnardi V, Zambon A, Arico S. Exploring the dose-response relationship between alcohol consumption and the risk of several alcohol-related conditions: a meta-analysis. Addiction 1999;94:1551-1573.
70. Ariens GA, van Mechelen W, Bongers PM, Bouter LM, van der Wal G. Physical risk factors for neck pain. Scand J Work, Environ Health 2000;26:7-19.
71. Carruthers SG, Larochelle P, Haynes RB, Petrasovits A, Schiffrin EL. Report of the Canadian Hypertension Society Consensus Conference: 1. Introduction. Can Med Assoc J 1993;149:289-293.
72. Laupacis A, Wells G, Richardson WS, Tugwell P. Users' guides to the medical literature. V. How to use an article about prognosis. Evidence-Based Medicine Working Group. JAMA 1994;272:234-237.
73. Levine M, Walter S, Lee H, Haines T, Holbrook A, Moyer V. Users' guides to the medical literature. IV. How to use an article about harm. Evidence-Based Medicine Working Group. JAMA 1994;271:1615-1619.
74. Angelillo IF, Villari P. Residential exposure to electromagnetic fields and childhood leukaemia: a meta-analysis. Bulletin of the World Health Organization 1999;77:906-915.
75. Sheps SB, Schechter MT. The assessment of diagnostic tests. A survey of current medical research. JAMA 1984;252:2418-2422.
76. Arroll B, Schechter MT, Sheps SB. The assessment of diagnostic tests: a comparison of medical literature in 1982 and 1985. J Gen Intern Med 1988;3:443-447.
77. Cochrane Methods Working Group on Systematic Review of Screening and Diagnostic Tests. Recommended Methods; 1996.
78. Lijmer JG, Mol BW, Heisterkamp S, et al. Empirical evidence of design-related bias in studies of diagnostic tests. JAMA 1999;282:1061-1066.
79. McCrory DC, Matchar DB, Bastian L, et al. Evaluation of Cervical Cytology. Evidence Report/Technology Assessment No. 5. Rockville, MD.: Agency for Health Care Policy and Research. AHCPR Publication No.99-E010; 1999.
80. Ross SD, Allen IE, Harrison KJ, Kvasz M, Connelly J, Sheinhait IA. Systematic Review of the Literature Regarding the Diagnosis of Sleep Apnea. Evidence Report/Technology Assessment No. 1. Rockville, MD.: Agency for Health Care Policy and Research; 1999.
81. Gyorkos TW, Tannenbaum TN, Abrahamowicz M, et al. An approach to the development of practice guidelines for community health interventions. Can J Public Health. Revue Canadienne De Sante Publique 1994;85 Suppl 1:S8-13.
82. Briss PA, Zaza S, Pappaioanou M, et al. Developing an evidence-based Guide to Community Preventive Services—methods. The Task Force on Community Preventive Services. Am J Prev Med 2000;18:35-43.
83. Greer N, Mosser G, Logan G, Halaas GW. A practical approach to evidence grading. Joint Commission J Qual Improv 2000;26:700-712.
84. Guyatt GH, Haynes RB, Jaeschke RZ, et al. Users' Guides to the Medical Literature: XXV. Evidence-based medicine: principles for applying the Users' Guides to patient care. Evidence-Based Medicine Working Group. JAMA 2000;284:1290-1296.
85. NHS Research and Development Centre of Evidence-Based Medicine. Levels of Evidence. Accessed January 12, 2001. Web Page. Available at:
86. Harris RP, Helfand M, Woolf SH, et al. Current methods of the U.S. Preventive Services Task Force: A review of the process. Am J Prev Med 2001;20:21-35.
87. How to read clinical journals: IV. To determine etiology or causation. Can Med Assoc J 1981;124:985-990.
88. Guyatt GH, Cook DJ, Sackett DL, Eckman M, Pauker S. Grades of recommendation for antithrombotic agents. Chest 1998;114:441S-444S.
89. Guyatt GH, Sackett DL, Sinclair JC, Hayward R, Cook DJ, Cook RJ. Users' guides to the medical literature. IX. A method for grading health care recommendations. Evidence-Based Medicine Working Group. JAMA 1995;274:1800-1804.
90. Hoogendoorn WE, van Poppel MN, Bongers PM, Koes BW, Bouter LM. Physical load during work and leisure time as risk factors for back pain. Scand J Work, Environ Health 1999;25:387-403.
91. Sackett DL, Straus SE, Richardson WS, et al. Evidence-Based Medicine: How to Practice and Teach EBM. London: Churchill Livingstone; 2000.
92. Lohr KN. Grading Articles and Evidence: Issues and Options. Final Guidance Paper. Final report submitted to the Agency for Health Care Policy and Research for Contract No. 290-97-0011, Task 2. Research Triangle Park, NC: Research Triangle Institute; 1998.
93. Cook DJ, Mulrow CD, Haynes RB. Systematic reviews: synthesis of best evidence for clinical decisions. Ann Intern Med 1997;126:376-380.

Return to Contents

Availability of Full Report

The full evidence report from which this summary was derived was prepared for the Agency for Healthcare Research and Quality by the Research Triangle Institute-University of North Carolina Evidence-based Practice Center under contract No. 290-97-0011. Print copies of this report are available free of charge from the AHRQ Publications Clearinghouse by calling 1-800-358-9295. Requestors should ask for Evidence Report/Technology Assessment No. 47, Systems to Rate the Strength of Scientific Evidence (AHRQ Publication No. 02-E016).

The Evidence Report is also online at the National Library of Medicine Bookshelf.

Return to Contents

Current as of March 2002
AHRQ Publication No. 02-E015


The information on this page is archived and provided for reference purposes only.


AHRQ Advancing Excellence in Health Care