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Evidence-Based Medicine Ratings

AJNR's peer reviewers are asked to assign an evidence-based medicine rating to all manuscripts they evaluate. Articles rated as Level 1 or Level 2 are highlighted in both the print and electronic table of contents to alert readers to these studies of note.

Levels of Evidence for Primary Research Question1
Study Type Diagnostic—Investigating a diagnostic test Prognostic—Investigating the effect of a patient characteristic on the outcome of a disease Therapeutic—Investigating the results of a treatment
Question Is this (early detection) test worthwhile? Is this diagnostic or monitoring test accurate? What is the natural history of the condition? Does this treatment help? What are the harms?6
Level 1
  • Randomized controlled trial
  • Testing of previously developed diagnostic criteria (consecutive patients with consistently applied reference standard and blinding)
  • Inception2 cohort study (all patients enrolled at an early, uniform point in the course of their disease)
  • Randomized controlled trial
Level 2
  • Prospective2 cohort3 study
  • Development of diagnostic criteria (consecutive patients with consistently applied reference standard and blinding)
  • Prospective2 cohort3 study (patients enrolled at different points in their disease)
  • Control arm of randomized trial
  • Prospective2 cohort3 study
  • Observational study with dramatic effect
Level 3
  • Retrospective4 cohort3 study
  • Case-control5 study
  • Nonconsecutive patients
  • No consistently applied reference standard
  • Retrospective4 cohort3 study
  • Case-control5 study
  • Retrospective4 cohort3 study
  • Case-control5 study
Level 4
  • Case series
  • Poor or nonindependent reference standard
  • Case series
  • Case series
  • Historically controlled study
Level 5
  • Mechanism-based reasoning
  • Mechanism-based reasoning
  • Mechanism-based reasoning
  • Mechanism-based reasoning
  1. Level-1 through 4 studies may be graded downward on the basis of study quality, imprecision, indirectness, or inconsistency between studies or because the effect size is very small; these studies may be graded upward if there is a dramatic effect size. For example, a high-quality randomized controlled trial (RCT) should have ≥80% follow-up, blinding, and proper randomization. The Level of Evidence assigned to systematic reviews reflects the ranking of studies included in the review (i.e., a systematic review of Level-2 studies is Level 2). A complete assessment of the quality of individual studies requires critical appraisal of all aspects of study design.
  2. Investigators formulated the study question before the first patient was enrolled.
  3. In these studies, "cohort" refers to a nonrandomized comparative study. For therapeutic studies, patients treated one way (eg, coil) are compared with those treated differently (eg, coil and stent).
  4. Investigators formulated the study question after the first patient was enrolled.
  5. Patients identified for the study on the basis of their outcome (eg, failed coiling), called "cases," are compared with those who did not have the outcome (eg, successful coiling), called "controls."
  6. Sufficient numbers are required to rule out a common harm (affects >20% of participants). For long-term harms, follow-up duration must be sufficient.

Portions of this chart used with permission from The Journal of Bone and Joint Surgery Inc.

Click here to read more about evidence-based medicine in diagnostic imaging in: García Villar C. Evidence-based radiology for diagnostic imaging, What it is and how to practice it Radiología 2011;53:326-34

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