Table 1 Categorization of systematic error (bias) of clinical intervention studies into levels of evidence
From: Evidence at a glance: error matrix approach for overviewing available evidence
Category | Studies |
|---|---|
Level 1a | Meta-analysis of randomized trials with low risk of bias |
Level 1b | Randomized trial with low risk of bias |
Level 1c | Meta-analysis of all randomized trials |
Level 1d | Randomized trial with high risk of bias |
Level 2a | Meta-analysis of cohort studies |
Level 2b | Cohort study |
Level 3a | Meta-analysis of case-control studies |
Level 3b | Case-control study |
Level 4 | Case-series |
Level 5 | Expert opinion |