Levels of evidence as adopted by ASSI

Types of Studies
Therapeutic Studies – Investigating the results of treatment Prognostic Studies – Investigating the effect of a patient characteristic on the outcome of disease Diagnostic Studies – Investigating a diagnostic test Economic and Decision Analyses – Developing an economic or decision model
Level I
  • High quality randomized trial with statistically significant difference or no statistically significant difference but narrow confidence intervals
  • Systematic Review 2 of Level I RCTs (and study results were homogenous 3)
  • High quality prospective study 4 (all patients were enrolled at the same point in their disease with ≥ 80% follow  up of enrolled patients)
  • Systematic review 2 of Level I studies
  • Testing of previously developed diagnostic criteria on consecutive patients (with universally applied reference “gold” standard)
  • Systematic review 2 of Level I studies
  • Sensible costs and alternatives; values obtained from many studies; with multiway sensitivity analyses
  • Systematic review 2 of Level I studies
Level II
  • Lesser quality RCT (e.g. < 80% follow  up, no blinding, or improper randomization)
  • Prospective 4 comparative study 5
  • Systematic review 2 of Level II studies or Level 1 studies with inconsistent results
  • Retrospective 6 study
  • Untreated controls from an RCT
  • Lesser quality prospective study (e.g. patients enrolled at different points in their disease or <80% follow-up.)
  • Systematic review 2 of Level II studies
  • Development of diagnostic criteria on consecutive patients (with universally applied reference “gold” standard)
  • Systematic review 2 of Level II studies
  • Sensible costs and alternatives; values obtained from limited studies; with multiway sensitivity analyses
  • Systematic review 2 of Level II studies
Level III
  • Case control study7
  • Retrospective 6 comparative study 5
  • Systematic review 2 of Level III studies
  • Case control study 7
  • Study of nonS consecutive patients; without consistently applied reference “gold” standard
  • Systematic review 2 of Level III studies
  • Analyses based on limited alternatives and costs; and poor estimates
  • Systematic review 2 of Level III studies
Level IV Case Series 8 Case series
  • Case-control study
  • Poor reference standard
  • Analyses with no sensitivity analyses
Level V Expert Opinion Expert Opinion Expert Opinion Expert Opinion
  • A complete assessment of quality of individual studies requires critical appraisal of all aspects of the study design.
  • A combination of results from two or more prior studies.
  • Studies provided consistent results.
  • Study was started before the first patient enrolled.
  • Patients treated one way (e.g. cemented hip arthroplasty) compared with a group of patients treated in another way (e.g. uncemented hip arthroplasty) at the same institution.
  • The study was started after the first patient enrolled.
  • Patients identified for the study based on their outcome, called “cases”; e.g. failed total arthroplasty, are compared to those who did not have outcome, called “controls”; e.g. successful total hip arthroplasty.
  • Patients treated one way with no comparison group of patients treated in another way.