Rating

How do the ratings from one research design compare with another? Designation of Levels of Evidence

PsycBITE includes studies with all levels of evidence described by the National Health and Medical Research Council.

It is noted that "a methodologically poor randomised trial (level II) may, however, provide a weaker basis for a recommendation than a high-quality observational study without randomisation, which can provide level III-2 evidence" (NHMRC, 1999, p.15). This means that an RCT (level II) with a score of 3 may be less methodologically sound than a non-RCT with a score of 6. For further information on Levels of Evidence see the NHMRC website.

Oxford Centre for Evidence-Based Medicine 2011 Levels of Evidence

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 randomized trial* Case-series or case- control studies, or poor quality prognostic cohort study** n/a
Does this intervention help?
(Treatment Benefits)
Systematic review of randomized trials or n-of-1 trials Randomized trial or observational study with dramatic effect Non-randomized 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 randomized 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 randomized trial or (exceptionally) observational study with dramatic effect Non-randomized 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 randomized trials or n-of-1 trial Randomized trial or (exceptionally) observational study with dramatic effect
Is this (early detection) test worthwhile?
(Screening)
Systematic review of randomized trials Randomized trial Non -randomized controlled cohort/follow-up study** Case-series, case-control, or historically controlled studies** Mechanism-based reasoning

* Level may be graded down on the basis of study quality, imprecision, indirectness (study PICO 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.

** As always, a systematic review is generally better than an individual study.

OCEBM Levels of Evidence Working Group*. 'The Oxford 2011 Levels of Evidence'. Oxford Centre for Evidence-Based Medicine.

http://www.cebm.net/index.aspx?o=5653

* OCEBM Table of Evidence Working Group = Jeremy Howick, Iain Chalmers (James Lind Library), Paul Glasziou, Trish Greenhalgh, Carl Heneghan, Alessandro Liberati, Ivan Moschetti, Bob Phillips, Hazel Thornton, Olive Goddard and Mary Hodgkinson