Table 1:

Levels of evidence for studies of the accuracy of diagnostic testsa

Levels of EvidenceType of Evidence
IaSystematic review (with homogeneity)b of level-1 studiesc
IbLevel-1 studiesc
IILevel-2 studiesd
Systematic reviews of level-2 studies
IIILevel-3 studiese
Systematic reviews of level-3 studies
IVConsensus, expert committee reports or opinions and/or clinical experience without explicit critical appraisal; or based on physiology, bench research, or “first principles”
  • a Adapted from The Oxford Centre for Evidence-Based Medicine Levels of Evidence (2001) and the Centre for Reviews and Dissemination Report Number 4 (2001). Copyright National Institute for Health and Care Excellence February 2004.

  • b Homogeneity means there are no or minor variations in the directions and degrees of results between individual studies that are included in the systematic review.

  • c Level-1 studies are studies:

    • •  that use a blind comparison of the test with a validated reference standard.

    • •  in a sample of patients that reflects the population to whom the test would apply.

  • d Level-2 studies are studies that have only 1 of the following:

    • •  narrow population (the sample does not reflect the population to whom the test would apply).

    • •  use a poor reference standard (defined as that where the “test” is included in the “reference,” or where the “testing” affects the “reference”).

    • •  the comparison between the test and reference standard is not blind.

    • •  case-control studies.

  • e Level-3 studies are studies that have at least 2 or 3 of the features listed above.