Not all research evidence is the same. There are lots of ways to study a health condition or intervention. The study design influences the quality of evidence. Pyramids are often used to show the quality of different types of studies. To find the best evidence, start with resources at the top of the pyramid.
This first pyramid gives a broad overview of the relative quality of different types of evidence to support clinical decision-making: studies, synopses, syntheses, summaries and systems.
For more information, check out this webpage from McMaster University.
This pyramid shows the relative quality of different types of study designs. For example, randomized-controlled studies typically provide better evidence than observational studies, such as case control and cohort studies.