The key to figuring out the appropriate level of evidence for a given study is to examine its methods and assess its design. Below, we've linked to selections from a useful series of articles by Ranganathan and Aggarwal detailing different study design types (their methods, the forms of evidence they produce, etc.). Use these articles to help you understand the specialized language of study design.
You may also find the Centre for Evidence-Based Medicine's (CEBM) brief study design article helpful.
If you are on a mobile device and are viewing this research guide from within a Blackboard course site, click here for a better site view.
The figure below is an adaptation of the levels of evidence as presented by Melnyk and Fineout-Overholt (2015, p.11). According to the authors, these levels should be viewed hierarchically in terms of objective reliability and generalizability; with Level I representing the most generalizable and objective evidence, and Level VII representing the least generalizable evidence with a greater risk of bias (p.92).
Levels of Evidence and PICOT charts adapted from:
Melnyk, B. Mazurek, & Fineout-Overholt, E. (2015). Evidence-based practice in nursing and healthcare: a guide to best practice. Third edition. Philadelphia: Wolters Kluwer Health
Levels of Evidence Flowchart courtesy of the University of Michigan libraries (2018), made available under a Creative Commons Attribution 4.0 license (CC BY 4.0).