A Critical Appraisal on the "Level-of-evidence" Classification Systems.

Evidence-based medicine is about analyzing the evidence and then utilizing the same analysis in making clinical decisions. The key element of evidence-based medicine is the hierarchical system of categorizing evidence. This hierarchy is known as the "levels of evidence".1 Clinicians use this classification to identify the highest level of evidence to answer clinical questions. Various types of research studies answer the different kinds of clinical questions.1.