The Levels of Evidence

Introduction

Level of evidence is a cornerstone of evidence-based practice in which evidence is classified hierarchically to solve a clinical question. This heuristic is employed to order the relative strength (grade) of results derived from scientific study. Levels of evidence are based on the methodological quality and validity of scientific studies (Dang & Dearholt, 2018). The main types of evidence are random controlled trials, systematic review, critically appraised topics and articles, cohort studies, case studies, and expert opinion.

Levels of Evidence

Level 1:  a) Involves evidence obtained from high quality systematic review of pertinent randomized controlled trials (RCT). RCT are characterized by use of randomization, treatment and control, blinding (Dang, & Dearholt, 2018).

b) Evidence obtained from individual RCT with narrow confidence interval and low risk of bias.

c) Evidence obtained from all non RCTs

Level II:  a) Evidence derived from one or more well-designed controlled study lacking randomization

 b) Evidence derived from one or more other kinds of well-designed quasi-experimental study.

Level III: evidence derived from non-experimental descriptive studies like cohort studies, case studies and correlational studies

Level IV: evidence obtained from review of qualitative and descriptive studies

Level V: evidence obtained from expert opinion of respected authorities, such as consensus guidelines, report of expert committees. Examples are clinical practice guidelines and consensus panels (Roever et. al.2016).

Levels of evidence from at least one study offer the strength of recommendation for a specific practice. The grading system is used to provide the strength of recommendations for key recommendations in levels of evidence. Grades are given based on the consistency and quality of existing evidence. The grades are A, B, C, and D. A strong recommendation (grade A) is assigned when there is either level I evidence or consistent findings from numerous studies of levels II, III and IV. This means that, unless there is a compelling rationale for alternative approach, healthcare providers must follow a strong recommendation because evidence support it. Grade A indicate there is good evidence to recommend the clinical practice or action (Roever et. al.2016)

            Grade B recommendation is assigned when there is levels II, III, or IV evidence (moderate evidence) and the findings are consistent. The implication for this in practice is that medical professionals are needed to follow a recommendation while remaining vigilant to new information. Grade B recommendation indicates fair evidence to recommend the practice or action. Grade C recommendation is given when there is levels II, III, or IV evidence (weak evidence) but the findings are generally inconsistent. The assignment of grade c implies the available evidence is conflict, preventing clinicians to recommend for or against the practice.  This requires the medical professionals to be bendable in their decision making concerning appropriate practice. In addition to that patient preference play an influential role in decision making. Grade D is assigned when there is level V evidence (conflicting) and little systematic empirical evidence. There is fair evidence to recommend against the clinical practice or action. This means that the medical professionals should take into account all options in decision making. They should also be alert to new evidence that elucidates the balance of benefit v. harm.       

References

Dang, D., & Dearholt, S.L. (2018). Johns Hopkins nursing evidence-based practice : Model & guidelines (3rd ed). Sigma Theta Tau International.

Roever, L. et al. (2016).Degrees of Recommendations and Levels of Evidence: What you Need to Know?  Evidence Based Medicine and Practice 2(2) DOI: 10.4172/2471-9919.1000101