Evidence-based medicine (EBM) searches for evidence and uses that evidence to make clinical decisions. A cornerstone of EBM is the hierarchical system of classifying evidence known as the levels of evidence. Levels of evidence (LOE) are used to describe the strength of the results measured in a clinical trial or research study. The higher the level, the more reliable the evidence is assumed to be. LOE models review data based on the elements of design, quality, and consistency of evidence.
Start at the top of the pyramid for the most reliable evidence, keeping in mind that research may not yet exist or may not be feasible for some questions. Knowing the level of evidence for which you are searching may assist you in crafting an appropriate search strategy on your topic. A frequently used system in medicine is from the Oxford Center for Evidence-Based Medicine, a site of a World Health Organization (WHO)collaborating center.