Skip to main content

Table 2 Oxford Centre for Evidence-based Medicine (OCEBM) levels of evidence (2011) [45]

From: The European guideline on management of major bleeding and coagulopathy following trauma: fifth edition

Question Step 1 (level 1*) Step 2 (level 2*) Step 3 (level 3*) Step 4 (level 4*) Step 5 (level 5)
How common is the problem? Local and current random sample surveys (or censuses) Systematic review of surveys that allow matching to local circumstances** Local non-random sample** Case-series** N/A
Is this diagnostic or monitoring test accurate? (diagnosis) Systematic review of cross-sectional studies with consistently applied reference standard and blinding Individual cross-sectional studies with consistently applied reference standard and blinding Non-consecutive studies or studies without consistently applied reference standards** Case-control studies or poor or non-independent reference standard** Mechanism-based reasoning
What will happen if we do not add a therapy? (prognosis) Systematic review of inception cohort studies Inception cohort studies Cohort study or control arm of randomised trial* Case-series or case-control studies or poor-quality prognostic cohort study** N/A
Does this intervention help? (treatment benefits) Systematic review of randomised trials or n-of-1 trials Randomised trial or observational study with dramatic effect Non-randomised controlled cohort/follow-up study** Case-series, case-control studies or historically controlled studies** Mechanism-based reasoning
What are the common harms? (treatment harms) Systematic review of randomised trials, systematic review of nested case-control studies, n-of-1 trial with the patient you are raising the question about, or observational study with dramatic effect Individual randomised trial or (exceptionally) observational study with dramatic effect Non-randomised controlled cohort/follow-up study (post-marketing surveillance) provided there are sufficient numbers to rule out a common harm. (For long-term harms the duration of follow-up must be sufficient.)** Case-series, case-control or historically controlled studies** Mechanism-based reasoning
What are the rare harms? (treatment harms) Systematic review of randomised trials or n-of-1 trial Randomised trial or (exceptionally) observational study with dramatic effect
Is this (early detection) test worthwhile? (screening) Systematic review of randomised trials Randomised trial Non-randomised controlled cohort/follow-up study** Case-series, case-control or historically controlled studies** Mechanism-based reasoning
  1. *Level may be graded down on the basis of study quality, imprecision, indirectness [study PICO (patient, problem or population, intervention, comparison, control or comparator, outcome) does not match questions PICO)], because of inconsistency between studies, or because the absolute effect size is very small; level may be graded up if there is a large or very large effect size
  2. **As always, a systematic review is generally better than an individual study
  3. N/A not applicable