Using the 6S Pyramid to Find the Best Evidence


6S Pyramid for Finding the Best Evidence

6S Pyramid for Finding the Best Evidence

Whether you’ve got a research paper to write or you are looking for best evidence for a specific intervention, you’ve got to search for the evidence to make or back up your arguments, right? Presumably, you’ve answered your background questions and have your foreground question in a PICO format.

You’ve written your PICO question to help you search more efficiently – that’s the first step. But now, how can you spend the least amount of time finding the best evidence, and still fulfill your goals?  You spend your time searching in the right places, of course! The 6S Pyramid is your answer.

Your PICO question will point you toward the key terms to use in your search strategy. But instead of searching the CINAHL or MEDLINE database from your university or hospital library, you need to start at the top of the evidence hierarchy. The 6S pyramid will help you answer your foreground questions by looking in the right places for the answers.

I introduced you to the 6S Pyramid very briefly in the post on the 6A’s of evidence-based practice. This post will explain how this model came about, its purpose, the different evidence levels, and how it will help you in your search for the best evidence.  

What is the 6S Pyramid?

The 6S Pyramid was conceived and modified as evidence sources evolved by physicians, nurses, and a librarian at McMaster University in Hamilton, Ontario, Canada (DiCenso, Bayley, & Haynes, 2009; Haynes, 2007). (FYI – McMaster University is ground zero for the EBP movement in North America.) The resulting model is a helpful resource for you to find answers to your Foreground questions.

Haynes (2007) originally proposed a hierarchical model of pre-appraised evidence sources to depict a ranking of sources from the most rigorous methods and most helpful (i.e., the appraisal work is done for you, the source is valid) to the least helpful (i.e., you have to do your own work of appraising the evidence).

The model is shaped like a pyramid and evolved from 4 levels of evidence starting with the letter “S” (4S) to 5 levels (5S) and now to the 6S version. The purpose of the model is to help you see where you should be focusing your retrieval efforts. The most recent revision of this model, the “6S” version, is explained in this post and is based on the articles by Haynes (2007), DiCenso et al. (2009), and the McMaster University Nursing EBP webpages.

The purpose of the 6S Pyramid is to help you see where you should be focusing your retrieval efforts.

The idea behind the ranking of the 6S model is that information you receive from the higher levels or categories of evidence is stronger because the methods are more controlled, more standardized, and more rigorous. The stronger the research methods, the more confidence you can have in the results – therefore the higher the rank or level in the model. I know I repeat this statement in many posts – but my constant reiteration of this major point is important! I want this point to be ingrained in your minds! More importantly for busy clinicians, the evidence in the top levels of the pyramid are Preappraised – the work of critical appraisal is done for you.

The 6S categories are Systems, Summaries, Synopses of Syntheses, Syntheses, Synopses of Original Studies, and Original Studies.  The type of question you ask will help you determine which database might be most appropriate to search for answers. The Summaries level incorporates the levels beneath. I added the bottom level, Other Evidence Sources, to acknowledge the existence and use of non-research sources of evidence. I talked about evidence sources in the 6A’s post, so I won’t redefine those here. 

6S Pyramid for Finding the Best Evidence

6S Pyramid for Finding the Best Evidence

You’ll notice that I’ve divided the levels into pre-appraised and not pre-appraised.  I’ve also have a caveat (the asterisk *) that even if you find a study, let’s say a systematic review (a synthesis), from a database that is not one of the ones you “trust” to be credible, that you still have to vet the source. In other words, you still need to know that the process that the authors used to create the systematic review was robust.  Then you can feel confident in using the research results in practice.  I talked about what it means for evidence to be pre-appraised or pre-filtered in last week’s post, so I’ll refer you back to that post if you need a refresher.

Let’s discuss the different levels of the 6S Pyramid and I’ll point you toward credible sources for each level.

The 6S Pyramid of Evidence Quality: Start Your Search at the Top!

For the greatest efficiency, you should always begin your literature searches at the highest level of evidence and work downwards (Haynes, 2007). 

Identify the search terms from your PICO question. Craft a search strategy. Choose your databases. Go. 

For the greatest efficiency, you should always begin your searches at the highest level of evidence and work downwards (Haynes, 2007). 


The best evidence possible is that which includes all the levels of evidence integrated into one clinical system, such as the integration of a hospital electronic medical record system with best evidence guidelines, textbooks, and other research and non-research sources of evidence.  See the post on Best Evidence for a list of what constitutes evidence in EBP. 

Having a system that would automatically clue you into the best treatment plan for your patients, after you enter their physical assessment data and personal information, is the ultimate BEST EVIDENCE system! This would be a massive knowledge-based clinical decision support system. According to AHRQ, “clinical decision support (CDS) provides timely information, usually at the point of care, to help inform decisions about a patient’s care.” 

This CDS system would provide “pop-up alerts to the potential drug interaction when the [provider] prescribed the new medicine; clinical prediction rules to assess the [specific] risks … ; clinical guidelines for treatment of [the patient’s condition]; [and] reminders for timely followup” (Berner, 2009, p. 4). But… this type of institutional system costs a lot of money and time and manpower. These systems are just beginning to be implemented in some settings, but it will take a long time before a knowledge-based CDS is standard in every healthcare facility. If you work at such an institution, let me know! 

Acknowledging that few institutions have the highest level of quality evidence (i.e., computerized, evidence-based, decision support systems) available to them, the clinician will usually focus on the remaining levels of evidence to search for the answers to their clinical practice questions (Haynes, 2007). 

NOTE: Examples of online resources for summaries, synopses, and syntheses is found in the post on Pre-Appraised Evidence. Additional online resources for summaries is found in the Clinical Practice Guidelines resources post. I’ll also note some additional resources not identified in the linked posts. 


The highest level of quality evidence accessible to all clinicians is Summary evidence. Summaries are evidence-based sources that are vetted by experts (i.e., pre-appraised) and updated regularly to accommodate the newest evidence. Clinical practice guidelines (CPGs) and online evidence-based clinical texts are the mainstays of this level. I provided a list of online CPG websites and other pre-appraised evidence sources in previous posts.

Synopses of Syntheses

Synopses of syntheses are summaries of systematic reviews.  Because of the increase in the number and type of reliable clinical topic evidence sources, the “6S” hierarchy of quality evidence differentiates the synopses evidence into two strength layers.  The synopses of syntheses layer was added to emphasize the fact that synopses of syntheses (that is, synopses or summations of systematic reviews) provide a stronger level of evidence than synopses of single studies (DiCenso et al., 2009).

Synopses of syntheses can be found in journals that focus on evidence-based practice. These journals are called secondary journals or abstract journals because they abstract information from the systematic review for the study overview and then provide a commentary on the research methods and practice implications. 

Sources of synopses of syntheses include National Institute for Health Research (NHS) Centre for Reviews and Dissemination (CRD) from the University of York,, and the Cochrane Collaboration. 

Secondary journals or abstract journals include Evidence-Based Nursing, Evidence-Based Medicine, Evidence-Based Mental Health, Evidence-Based Medicine, Evidence-Based Healthcare and Public Health, Evidence-Based Midwifery, Evidence-Based Obstetrics and GynecologyACP Journal Club, Ortho Evidence, and Cancer Treatment Reviews. 


Systematic reviews are a systematic and comprehensive, critical review of high-quality research studies on a specific clinical question. The data from those studies is crafted into an “answer” to the clinical question posed. Sources of syntheses include the Cochrane Library, the Campbell Collaboration, the NHS Centre for Reviews and Dissemination (CRD), and

Synopses of Original Studies

A synopsis of original or primary research is a summary or overview of one high-quality study. The synopsis usually is accompanied by a commentary on the quality of the methods and the implications for clinical practice.

The synopsis of original (single) studies level is the last level of pre-appraised evidence. The evidence-based abstract journals listed above are excellent sources of synopses of original studies.

Critically appraised topics (CATs) or Best Evidence Topics (BETs) are also helpful for finding information quickly. CATs and BETs are usually short answers written in a standardized format to a PICO question that may use one or more original research articles. There is a statement of methodological quality of the studies and a clinical bottom line answer. CATs also may be an actual critical appraisal of a specific research study. You can find BETs and CATs related to emergency care, cardiothoracics, nursing, primary care, and pediatrics at BestBETs.

Original Studies

Original or primary research studies are those conducted by one or more researchers to scientifically discover the answer to clinical questions. Original research includes quantitative research designs (e.g., randomized controlled trials, observational studies, epidemiologic designs, case reports), qualitative designs (e.g., phenomenology, grounded theory, ethnography), and mixed method designs. 

There are many databases from which you can find primary research studies. In fact, these are the databases that are typically searched FIRST. Realize that searching these databases first means that you are beginning your search at the bottom of the pyramid, not the top!  

I’m sure you are familiar with a few of these search databases like CINAHL (Cumulative Index to Nursing and Allied Health), PubMed (provided by the National Library of Medicine), and MEDLINE.  There’s also PubMed Clinical Queries for specific queries; EMBASE (Excerpta Medica dataBASE) includes European journals and drug/pharmacy coverage; PsycINFO (psychology); AMED (Allied and Complementary Medicine Database) is produced by the British Library and covers allied health (physiotherapy, occupational therapy, rehabilitation, speech and language therapy, podiatry) as well as complementary medicine and palliative care; ERIC (Education Resources Information Center) is provided by the U.S. Department of Education and contains literature on education and educational research; and Health Services Research (HSR) Queries

You can also search for original and secondary studies using several free databases. You can register for a free or paid account at SUMsearchTRIP (Turning Research Into Practice), ACCESSSS was created by the folks at McMasters PLUS (Premium LiteratUre Service), PubMedHealth, and Health Services/Technology Assessment Texts (HSTAT).

Original studies are not pre-appraised evidence.  Original research is reported in clinical and professional journals. And while most journals have editorial boards and manuscript reviewers to assess research reports before they are published. There is no commentary of a critical appraisal of the research methods by an external source attached to the published study. There is no expert to help you determine if the research methods were valid. Therefore, you will have to critically appraise the research study yourself. You have to determine if the methods are strong enough for you to believe the results. 

Hey, this is not the end of the world! If there is no evidence on the topic you are interested in the higher levels of the pyramid, then you might have to look for primary research to get an answer to your question. You can use tools to critically appraise primary research and come up with your conclusion.  The point is that this takes time to do. 

Other Evidence Sources

This is the level I added to the diagram so you don’t forget that there are many types of evidence that can be used in addition to research. Data from patient records, benchmark data, risk data, clinician group practices, pathophysiology, and other sources of non-research data comprise this category. Again, see the post on Best Evidence for a list of what constitutes evidence in EBP. 

I highly recommend you to use this 6S Pyramid to help you work on your school papers and your evidence-based practice projects.


You’ll find relevant data in a more efficient manner.  



You’ll never search the literature the same way again!


Berner, E. S. (2009, June). Clinical decision support systems: State of the art. AHRQ Publication No. 09-0069-EF. Rockville, MD: Agency for Healthcare Research and Quality. Retrieved from

DiCenso, A., Bayley, L., & Haynes, R. B. (2009). Accessing pre-appraised evidence: Finetuning the 5S model into a 6S model. Evidence-Based Nursing, 12(4)99-101. doi:10.1136/ebn.12.4.99-b 

Haynes, R. B. (2007). Of studies, syntheses, synopses, summaries, and systems: The “5S” evolution of information services for evidence-based health care decisions. Evidence-Based Nursing, 10(1), 6-7.