Table 1. Levels of Evidence For Primary Research Question

 

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 testEconomic

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 of Level I RCTs (and study results were homogenous
  • High quality prospective study (all patients were enrolled at the same point in their disease with ?80% follow-up of enrolled patients)

  • Systematic review of Level I studies
  • Testing of previously developed diagnostic criteria on consecutive patients (with universally applied reference "gold" standard)

  • Systematic review of Level I studies
  • Sensible costs and alternatives; values obtained from many studies; with multiway sensitivity analyses

  • Systematic review2 of Level I studies

Level II

  • Lesser quality RCT (eg, <80% follow-up, no blinding, or improper randomization)

  • Prospective comparative study{^}5

  • Systematic review of Level II studies or Level I studies with inconsistent results
  • Retrospective study

  • Untreated controls from an RCT

  • Lesser quality prospective study (eg, patients enrolled at different points in their disease or <80% follow-up)

  • Systematic review2 of Level II studies
  • Development of diagnostic criteria on consecutive patients (with universally applied reference “gold” standard)


    Systematic review of Level II studies
  • Sensible costs and alternatives; values obtained from limited studies; with multiway sensitivity analyses

  • Systematic review of Level II studies

Level III

  • Case control study

  • Retrospective comparative study

  • Systematic review of Level III studies
  • Case control study
  • Study of non-consecutive patients; without consistently applied reference “gold” standard

  • Systematic review of Level III studies
  • Analyses based on limited alternatives and costs; and poor estimates

  • Systematic review of Level III studies

Level IV

  • Case series
  • Case series
  • Case-control study

  • Poor reference standard
  • Analyses with no sensitivity analyses

Level V

  • Expert opinion
  • Expert opinion
  • Expert opinion
  • Expert opinion

Notes

  1. Complete assessment of quality of individual studies requires critical appraisal of all aspects of study design
  2. A combination of results from two or more prior studies
  3. Studies provided consistent results
  4. Study was started before the first patient enrolled
  5. Patients treated one way (eg, cemented hip arthroplasty) compared with a group of patients treated in another way (eg, uncemented hip arthroplasty) at the same institution
  6. The study was started after the first patient enrolled
  7. Patients identified for the study based on their outcome, called “cases” — eg, failed total arthroplasty — are compared to those who did not have outcome, called “controls” — eg, successful total hip arthroplasty
  8. Patients treated one way with no comparison group of patients treated in another way