# Hierarchy of Medical Evidence There are different levels of evidence regarding clinical research. Starting from the weakest and going to the strongest: 1. Case Reports 2. Case Series 3. Database Studies 4. Observational Studies 1. Case-Control / Retrospective 2. Cross-sectional 3. Cohort / Prospective 5. Experimental Studies (i.e. [[Clinical Trial|clinical trials]]) 1. Historical controls 2. Non-randomized 3. Randomized Experimental studies are the only type of evidence that can provide evidence for a cause-effect relationship between a treatment and some outcome related to a disease. Everything else is contaminated by [[Confounders|confounders]]. --- # References - Wallace, S. S., Barak, G., Truong, G., & Parker, M. W. (2022). Hierarchy of Evidence Within the Medical Literature. In Hospital Pediatrics (Vol. 12, Issue 8, pp. 745–750). American Academy of Pediatrics (AAP). https://doi.org/10.1542/hpeds.2022-006690