Table 2-1Levels of evidence for studies of accuracy of diagnostic tests (reproduced by kind permission from the NICE guidelines manual (April 2007))

Level of evidenceType of evidence
1aSystematic review with homogeneity (a) of level-1 studies (b)
1bLevel-1 studies (b)
IILevel-2 studies (c)
Systematic reviews of level-2 studies
IIILevel-3 studies (d)
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’

Homogeneity indicates there are none or minor variations in the directions and degrees of results between individual studies included in the systematic review


Level-1 studies:

  • Use a blind comparison of the test with a reference standard (gold standard)
  • Are conducted in a sample of patients that reflects the population to whom the test would apply

Level-2 studies have only one of the following:


Level-3 studies have two or three of the above features

From: 2, Methodology

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NICE Clinical Guidelines, No. 85.
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