Table 2-3Levels 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’
a

Homogeneity indicates there are no or minor variations in the directions and degrees of results between individual studies included in the systematic review

b

Level-1 studies:

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

c

Level-2 studies have only one of the following:

  1. Narrow population (sample does not reflect the population to whom the test would apply)
  2. A poor reference standard (where tests are not independent)
  3. The comparison between the test and reference standard is not masked

d

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

From: 2, Methodology

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The Management of Lower Urinary Tract Symptoms in Men [Internet].
NICE Clinical Guidelines, No. 97.
National Clinical Guideline Centre (UK).
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