Guide to Research Methods - The Evidence Pyramid
MEDLINE and the other online medical literature databases try to be as comprehensive as possible in their coverage. As a result, indexed material may have little direct application to present-day medical practice.
The different types of material indexed in MEDLINE are labelled in the pyramid diagram, with the least clinically relevant at the bottom and the most clinically relevant at the top. The four layers above case reports and case series represent actual clinical research; the layers below are least clinically relevant and can be useful as background resources.
The next few pages provide basic definitions and examples of clinical research designs to help the medical student or new clinician understand how the design of a research study may affect whether or not to accept its findings in caring for a patient.
More detail on each level is available by reading the pages in sequential order or by clicking on any level of the pyramid or by selecting from the topics below: