Levels of Evidence for Primary Research Question.
| Types of Studies | ||||
|---|---|---|---|---|
| Therapeutic Studies Investigating the Results of Treatment | Prognostic Studies Investigating the Outcome of Disease | Diagnostic Studies Investigating a Diagnostic Test | Economic and Decision Analyses Developing an Economic or Decision Model | |
| Level I | 1. Randomized controlled trial a. Significant difference b. No significant difference but narrow confidence intervals 2. Systematic review2 of Level-I randomized controlled trials (studies were homogeneous) | 1. Prospective study1
2. Systematic review2 of Level-I studies | 1. Testing of previously developed diagnostic criteria in series of consecutive patients (with universally applied reference “gold” standard) 2. Systematic review2 of Level-I studies | 1. Clinically sensible costs and alternatives; values obtained from many studies; multiway sensitivity analyses 2. Systematic review2 of Level-I studies |
| Level II | 1. Prospective cohort study3
2. Poor-quality randomized controlled trial (e.g., <80% follow-up) 3. Systematic review2 a. Level-II studies b. nonhomogeneous Level-I studies | 1. Retrospective study4 2. Study of untreated controls from a previous randomized controlled trial 3. Systematic review of Level-II studies | 1. Development of diagnostic criteria on basis of consective patients (with universally applied reference “gold” standard) 2. Systematic review2 of Level-II studies | 1. Clinically sensible costs and alternatives; values obtained from many studies; multiway sensitivity analyses 2. Systematic review2 of Level-II studies |
| Level III | 1. Case-control study5
2. Retrospective cohort study4 3. Systematic review2 of Level-III studies | 1. Study of non-consecutive patients (no consistently applied reference “gold” standard) 2. Systematic review2 of Level-III studies | 1. Limited alternatives and costs; poor estimates 2. Systematic review2 of Level-III studies | |
| Level IV | Case series (no, or historical, control group) | Case series | 1. Case-control study 2. Poor reference standard | No sensitivity analyses |
| Level V | Expert opinion | Expert opinion | Expert opinion | Expert opinion |
| 1. All patients were enrolled at the same point in their disease course (inception cohort) with ≥80% follow-up of enrolled patients. | ||||
| 2. A study of results from two or more previous studies. | ||||
| 3. Patients were compared with a control group of patients treated at the same time and institution. | ||||
| 4. The study was initiated after treatment was performed. | ||||
| 5. Patients with a particular outcome (“cases” with, for example, a failed total arthroplasty) were compared with those who did not have the outcome (“controls” with, for example, a total hip arthroplasty that did not fail). | ||||