This tutorial was developed by staff at Duke University Medical Center Library and the Health Sciences Library at the University of North Carolina at Chapel Hill. It is used with permission by Saint Louis University Medical Center Library.
This is what is known as the Evidence Based Pyramid. The higher you go in the pyramid, the stronger the evidence. So Systematic Reviews/Meta Analysis are at the top. Your question will determine what type of study you are looking for. This chart shows for each type of question, the highest level of evidence/type of study you are looking for.