Introduction Evidence-based medicine (EBM) involves using data derived from the scientific method to improve clinical decision-making In applying evidence to treat patients, physicians must understand which types of evidence to prioritize some evidence is more reliable than others based on study design and quality Levels of Evidence Level 1 (highest) 1a systemic review and/or meta-analysis of high-quality randomized control trials (RCTs) login to view 2 more bullets 1b single high-quality RCT login to view 1 more bullet Level 2 2a high quality non-randomized control trials 2b high quality cohort studies login to view 4 more bullets Level 3 case-control studies studies in which patients are assigned to groups in a non-random fashion by their outcome status (e.g., diseased or not-diseased) and examined for the prior exposure of interest Level 4 cross-sectional studies study in which exposure and outcome are assessed simultaneously case series a report of multiple patients with the same disease or treatment but no control group or comparison group Level 5 case report detailed description of a single patient's symptoms, signs, treatment, and disease course expert opinion editorials