Evidence from well-designed case-control or cohort studies. Evidence from systematic reviews of descriptive and qualitative studies (meta-synthesis). Evidence from a single descriptive or qualitative study. Evidence from the opinion of authorities and/or reports of expert committees.
In most evidence hierachies current, well designed systematic reviews and meta-analyses are at the top of the pyramid, and expert opinion and anecdotal experience are at the bottom.
Level I: Evidence from a systematic review of all relevant randomized controlled trials. Level II: Evidence from a meta-analysis of all relevant randomized controlled trials.
C : The recommendation is based on expert opinion and panel consensus. X: There is evidence that the intervention is harmful.
Typically, systematic reviews of completed, high-quality randomized controlled trials – such as those published by the Cochrane Collaboration – rank as the highest quality of evidence above observational studies, while expert opinion and anecdotal experience are at the bottom level of evidence quality.
Level 1 . Randomized controlled trial (RCT) a study in which patients are randomly assigned to the treatment or control group and are followed prospectively.
Direct Evidence The most powerful type of evidence , direct evidence requires no inference. The evidence alone is the proof .
Both systems place randomized controlled trials (RCT) at the highest level and case series or expert opinions at the lowest level. The hierarchies rank studies according to the probability of bias. RCTs are given the highest level because they are designed to be unbiased and have less risk of systematic errors.
Narrative reviews , often just called Reviews , articles may be evidence -based, but they are not evidence . Rather than answering a specific clinical question, they provide an overview of the research landscape on a given topic.
We describe four levels of a qualitative hierarchy of evidence -for-practice. The least likely studies to produce good evidence -for-practice are single case studies , followed by descriptive studies that may provide helpful lists of quotations but do not offer detailed analysis.
Class of evidence (CoE) is a hierarchical rating system used by EBSJ and most major scientific publications for classifying the overall quality of an individual study. It is a shortcut to identifying what is likely the best (or worst) evidence on a given topic.
Examples of this type of research design include panel, cohort and case-control studies. Surveys and case studies are regarded as research designs with the greatest chance of bias in their outcome and therefore come low down in the hierarchy .
Level of Evidence B-R : Data derived from one or more randomized trials or meta-analysis of such studies. Level of Evidence B-NR: Data derived from one or more non-randomized trials or meta-analysis of such studies.
The system classifies quality of evidence (as reflected in confidence in estimates of effects) as high ( Grade A), moderate ( Grade B), or low ( Grade C) according to factors that include the risk of bias, precision of estimates, the consistency of the results, and the directness of the evidence .
How to rate the Quality of Evidence (your confidence in the effect estimate) High: We are very confident in the evidence supporting the recommendation. Further research is very unlikely to change the estimates of effect. Moderate: We are moderately confident in the evidence supporting the recommendation.