Skip to Main Content

Evidence-Based Medicine: 6S Hierarchy of EBM Resources

This is a libguide for praticing evidence-based medicine.

Categories of EBM Resources

The previous pages helped you decide what type of evidence is likely to answer your question. However, to know where to search for evidence, you need to understand how evidence is organized into categories of EBM resources.

DiCenso A, Bayley L, Haynes RB (2009). Accessing pre-appraised
evidence: fine-tuning the 5S model into a 6S model. Evidence-Based
Nursing, 12

The 6S Hierarchy of Evidence-Based Resources is a useful model for guiding clinical decision making.The model proposes six layers of evidence sources. The search for evidence-based resources should begin at the highest possible layer. The categories of EBM resources described here correspond to layers of the 6S model of EBM resources.

From a practical point of view, resources can be viewed in three broad categories: summaries and guidelines, pre-appraised research and non-appraised primary studies.

Categories of EBM Resources

Category Description Where to Find
Summaries and Guidelines

Online summaries provide the body of evidence at a topic level (not limited to a single question, intervention, or outcome). This also includes clinical practice guidelines with recommendations for clinical decision making.

ACP Smart Medicine & AHFS DI® Essentials™

BMJ Best Practice

DynaMed Plus


Natural Medicine

Pre-Appraised Resources Synopses of systematic reviews, systematic reviews and synopses of studies provide an assessment of an original study or a summary of a number of studies.


ACP Journal Club (now is Annals of Internal Medicine)

BMJ EvidenceAlerts

McMaster PLUS

Non-Appraised Primary Studies All primary studies with no pre-appraisal.




Embase - Ovid

Federated search (or meta search) engines allow searching for evidence across multiple resources (all levels of the 6S pyramid) at the same time. These tools retrieve evidence from summaries and pre-appraised and non-pre-appraised research and organize the results accordingly. Try these EBM search engines!



SumSearch 2