Levels of evidence used in Brain Trauma Foundation guidelines
| Level of evidence | Description |
|---|---|
| Class I | Evidence is derived from randomised controlled trials (RCTs). However, some may be poorly designed, lack sufficient patient numbers or suffer from other methodological inadequacies that render them Class II or III. |
| Class II | Evidence is derived from clinical studies in which data were collected prospectively, and retrospective analyses that were based on reliable data. Comparison of two or more groups must be clearly distinguished. Types of studies include observational, cohort, prevalence and case–control. Class II evidence may also be derived from flawed RCTs. |
| Class III | Evidence is derived from prospectively collected data that are observational and retrospectively collected data. Types of studies include case series, databases or registries, case reports and expert opinion. Class III evidence may also be derived from flawed RCTs, cohort or case–control studies. |
Levels of recommendation are Level I, II and III derived from Class I, II and III evidence, respectively.15