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Understanding and Applying Levels of Evidence Hierarchies

January 11, 2017

In December 2016, members of the Library Academic Partnership division of the Drexel University Libraries attended a presentation on understanding and applying levels of evidence hierarchies.

Levels of evidence hierarchy (sometimes called levels of evidence or hierarchy of evidence) are a ranking system used to describe the strength of the results being measured in a clinical trial or research study. Levels of evidence hierarchy can be applied to many fields but are typically used in the health sciences to rank or classify information (Burns PB, Rohrich RJ, Chung KC).

There are a number of hierarchies that are available across the globe, depending on specialization and specific use. This can lead to misinterpretation and confusion among consumers of this information. Questions concerning levels of evidence hierarchies are especially common in the practice of health sciences librarianship, and the topic is certainly murky.

During the session, various hierarchies were discussed, and visual aids were provided to demonstrate ways in which levels of evidence hierarchies can be used by the Libraries. These ranking systems can be of great use, as readers of ranked information do not have to personally appraise the data presented.

One of the key messages of the session was the fact that these rankings are not static. As more data and information is collected, a ranking can change. For example, a diagnostic test could initially receive a strong ranking for being a well-designed trial without randomization. This ranking might change if higher quality studies are performed at a later date (such as a well-designed trial with randomization).

Having participated in this short workshop, members of the Library Academic Partnership division of the Libraries are now well-prepared to work with levels of hierarchy. A similar presentation is available for interested Drexel students and faculty; please contact your liaison librarian for more details.

Burns PB, Rohrich RJ, Chung KC. Plast Reconstr Surg. 2011 Jul;128(1):305-10. doi: 10.1097/PRS.0b013e318219c171. The levels of evidence and their role in evidence-based medicine.

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