Evidence-based recommendations and guidance is the result of a careful review of studies and discussion by a panel of subject matter experts. For TCCC, the subject matter expert panels include both Committee on TCCC members and select invited subject matter experts from within both the military and civilian community, based on the specific interest area.

### Why the AHA Classification System?

The level of evidence classification combines an objective description of the existence and the types of studies supporting the recommendation and expert consensus, according to 1 of the following 3 categories:77

- Level of evidence A: recommendation based on evidence from multiple randomized trials or meta-analyses
- Level of evidence B: recommendation based on evidence from a single randomized trial or nonrandomized studies
- Level of evidence C: recommendation based on expert opinion, case studies, or standards of care.

The level of evidence recommendations allows readers to quickly glean information on the strength, certainty, and quality of evidence supporting each recommendation. The Level of Evidence (LOE) denotes the confidence in or certainty of the evidence supporting the recommendation, based on the type, size, quality, and consistency of pertinent research findings.78

A recommendation with level of evidence C does not imply that the recommendation is weak. Many important clinical questions addressed in guidelines do not lend themselves to clinical trials. Although, Randomized Clinical Trials are unavailable, there may be a very clear clinical consensus that a particular test or therapy is useful or effective.