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Toxicology Primer poison icon

NB: ECTR = extracorporeal treatment
Click here for levels of evidence

LevelTherapy / Prevention, Aetiology / HarmPrognosisDiagnosisDifferential diagnosis / symptom prevalence studyEconomic and decision analyses
1a SR (with homogeneity*) of RCTs SR (with homogeneity*) of inception cohort studies; CDR”  validated in different populations SR (with homogeneity*) of Level 1 diagnostic studies; CDR”  with 1b studies from different clinical centres SR (with homogeneity*) of prospective cohort studies SR (with homogeneity*) of Level 1 economic studies
1b Individual RCT (with narrow Confidence Interval”¡) Individual inception cohort study with > 80% follow-up; CDR”  validated in a single population Validating** cohort study with good” ” ”  reference standards; or CDR”  tested within one clinical centre Prospective cohort study with good follow-up**** Analysis based on clinically sensible costs or alternatives; systematic review(s) of the evidence; and including multi-way sensitivity analyses
1c All or none§ All or none case-series Absolute SpPins and SnNouts” “ All or none case-series Absolute better-value or worse-value analyses ” ” ” “
2a SR (with homogeneity*) of cohort studies SR (with homogeneity*) of either retrospective cohort studies or untreated control groups in RCTs SR (with homogeneity*) of Level >2 diagnostic studies SR (with homogeneity*) of 2b and better studies SR (with homogeneity*) of Level >2 economic studies
2b Individual cohort study (including low quality RCT; e.g., <80% follow-up) Retrospective cohort study or follow-up of untreated control patients in an RCT; Derivation of CDR”  or validated on split-sample§§§ only Exploratory** cohort study with good” ” ”  reference standards; CDR”  after derivation, or validated only on split-sample§§§ or databases Retrospective cohort study, or poor follow-up Analysis based on clinically sensible costs or alternatives; limited review(s) of the evidence, or single studies; and including multi-way sensitivity analyses
2c “Outcomes” Research; Ecological studies “Outcomes” Research   Ecological studies Audit or outcomes research
3a SR (with homogeneity*) of case-control studies   SR (with homogeneity*) of 3b and better studies SR (with homogeneity*) of 3b and better studies SR (with homogeneity*) of 3b and better studies
3b Individual Case-Control Study   Non-consecutive study; or without consistently applied reference standards Non-consecutive cohort study, or very limited population Analysis based on limited alternatives or costs, poor quality estimates of data, but including sensitivity analyses incorporating clinically sensible variations.
4 Case-series (and poor quality cohort and case-control studies§§) Case-series (and poor quality prognostic cohort studies***) Case-control study, poor or non-independent reference standard Case-series or superseded reference standards Analysis with no sensitivity analysis
5 Expert opinion without explicit critical appraisal, or based on physiology, bench research or “first principles” Expert opinion without explicit critical appraisal, or based on physiology, bench research or “first principles” Expert opinion without explicit critical appraisal, or based on physiology, bench research or “first principles” Expert opinion without explicit critical appraisal, or based on physiology, bench research or “first principles” Expert opinion without explicit critical appraisal, or based on economic theory or “first principles”
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