RATING SYSTEM FOR THE LEVEL/HIERARCHY OF EVIDENCE
LEVEL I: Evidence from an integrated literature review, systematic review or meta-analysis of all relevant randomized controlled trails (RCTs), or evidence-based clinical practice guidelines based on systematic reviews of RCTs.
· Review of research evidence related to a specific clinical question.
· Critically analyzes and synthesizes findings from multiple random control trials.
· Aim is to interpret and translate findings.
LEVEL II: Evidence obtained from at least one well-designated RCT. (experimental)
· Study subjects are randomly assigned to either a treatment or control group.
· May be:
· Blind: neither subject nor investigator knows which treatment the subject is receiving.
· Double-blind: neither subject nor investigator knows which treatment the subject is receiving.
· Non-blind: both subject and investigator know which treatment subject is receiving; used when it is felt that the knowledge of treatment is unimportant.
LEVEL III: Evidence obtained from well-designed controlled trials without randomization. (quasi-experimental)
· Always includes manipulation of an independent variable
· Lacks either random assignment or control group
· Findings must be considered in light of threats to validity (particularly selection)
LEVEL IV: Evidence from well-designed case-control and cohort studies.
· No manipulation of the independent variable.
LEVEL V: Evidence from systematic reviews of descriptive and qualitative studies, correlational studies.
LEVEL VI: Evidence from a single descriptive or qualitative study.
· Explorative in nature, such as interviews, observations, or focus groups.
· Starting point for studies of questions for which little research currently exists.
· Sample sizes are usually small and study results are used to design stronger studies that are more objective and quantifiable.
· Describing differences in variables between or among groups.
· Describing relationships among variables. No attempt to understand causal relationship.
LEVEL VII: Evidence from the opinion of authorities and/or reports of expert committees.
QUALITY DEFINITIONS
(Quality is based on Critical Appraisal)
GOOD: A study meets all research design-specific criteria well
FAIR: A study does not meet (or it is not clear that it meets) at least one design-specific criterion but has no known “fatal flaws”
POOR: A study that has at least one design specific “fatal flaw: or an accumulation of lesser flaws.
References
Dearholt, S.L.; & Dang, D. (2012). John Hopkins nursing-evidence based practice: model and guidelines (2nd ed.). John Hopkins University, School of Nursing: Sigma Theta Tau
Fineout-Overholt, E and Melnyk, B.M. (2005). Evidence-based practice in nursing and healthcare: a guide to best practice. Philadephia:Lippincott Williams and Wilkins.