Evidence is found in articles that have various types of methodology. A pyramid or step ladder, as visualized below, show the strength of each study methodology in comparison to other methodologies. The strongest level of evidence is at the top.
Evidence Step Ladder
Adapted by McMaster University Health Sciences Library from DiCenso A, Bayley L, Haynes RB. ACP Journal Club. Editorial: Accessing preappraised evidence: fine-tuning the 5S model into a 6S model. Ann Intern Med. 2009;151(6):JC3-3.