| Level |
Therapy/Prevention,
Aetiology/Harm |
Prognosis |
Diagnosis |
Differential
diagnosis/symptom prevalence study |
Economic
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" |