Table III.
Levels of evidence and grades of statement used in this Consensus Statement..
| Levels of evidence | ||
|---|---|---|
| 1a | Systematic review (with homogeneity) of Level-1 diagnostic studies; or clinical decision rule with Level-1b studies from different clinical centres | |
| 1b | Validating cohort study with good reference standards; or clinical decision rule tested within one clinical centre | |
| 1c | Absolute SpPins and SnNouts* | |
| 2a | Systematic review (with homogeneity) of Level > 2 diagnostic studies | |
| 2b | Exploratory cohort study with good reference standards; or clinical decision rule after derivation, or validated only on split-sample or databases | |
| 3a | Systematic review (with homogeneity) of studies Level ≥ 3b | |
| 3b | Non-consecutive study; or without consistently applied reference standards | |
| 4 | Case–control study, poor or non-independent reference standard | |
| 5 | Expert opinion without explicit critical appraisal, or based on physiology, bench research or ‘first principles’ | |
| Grades of statement | ||
| Code | Quality of evidence | Definition |
| A | High | Further research is very unlikely to change our confidence in the estimate of effect. ● Several high-quality studies with consistent results ● In special cases: one large, high-quality multicentre trial |
| B | Moderate | Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. ● One high-quality study ● Several studies with some limitations |
| C | Low | Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. ● One or more studies with severe limitations |
| D | Very low | Any estimate of effect is very uncertain. ● Expert opinion ● No direct research evidence ● One or more studies with very severe limitations |
Note: A minus sign ‘–‘ may be added to denote evidence that fails to provide a conclusive answer because it is either (a) a single result with a wide confidence interval; or (b) a systematic review with considerable heterogeneity. Such evidence is inconclusive, and therefore can only generate Grade D recommendations. *’Absolute SpPin’ is a diagnostic finding whose specificity is so high that a positive result rules in the diagnosis; ‘Absolute SnNout’ is a diagnostic finding whose sensitivity is so high that a negative result rules out the diagnosis.