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Evid Based Med 18:93-97 doi:10.1136/eb-2012-100995
  • Primer

Searching for the right evidence: how to answer your clinical questions using the 6S hierarchy

Editor's Choice
  1. Donna Windish
  1. Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA
  1. Correspondence to Donna Windish
    Department of Internal Medicine, Yale Primary Care Residency Program, Yale University School of Medicine, 64 Robbins Street, Waterbury, New Haven, CT 06708, USA; donna.windish{at}yale.edu
  • Accepted 6 August 2012
  • Published Online First 9 October 2012

Asking and answering clinical questions during daily practice can be challenging and time consuming. Knowing the resources available to answer a specific clinical question can lead to a more efficient and effective search strategy and thus, to a more applicable answer based on the levels of evidence available. This primer reviews how to search for the right evidence using a specified hierarchy and provides examples of pre-appraised resources with corresponding websites to help with your search.

Table 1

Clinical questions and available resources associated with the 6S model of evidence

Introduction

The readers of our journal most likely have busy clinical, administrative and/or teaching roles. As such, time is of the essence when thinking about answering clinical questions that arise in patient care. DiCenso and colleagues recently published a hierarchy of pre-appraised evidence called the 6S model.1 This model denotes in a pyramidal fashion the six levels of evidence available in clinical decision making. It starts with the largest resource available at the base of the pyramid with individual original studies. It then moves upward through synopses of studies, syntheses, synopses of syntheses, summaries and ends with the most specific form of evidence at the apex, with the “systems” layer. This article is a primer on how to use the 6S model when searching for and assessing the highest quality of evidence. The text and Table provide a summary view of clinical questions associated with each stage of the hierarchy, the strengths and weaknesses for each level of evidence, and a comprehensive list of pre-appraised resources with corresponding websites.

Studies (base of the pyramid)

Clinical question

I want to find the latest treatment for my patient's illness and want to use an evidence-based approach (ask, acquire, appraise and apply). Where should I look for this information?

Answer

In this case, searching the primary literature for single articles would be best.

Sample resources

PubMed; Clinical Queries; international literature searches through EMBASE; topics of nursing, biomedicine, health sciences librarianship, alternative/complementary medicine and consumer health through CINAHL; PsycINFO (see table 1 for corresponding websites of all sample resources in this article).

Strengths

The most updated studies are readily available both online and in print. Many of these resources provide alerts when new articles in a topic of interest are published.

Weaknesses

When using original studies, you need to understand how to use the search engines to find the study you are interested in and then subsequently interpret and apply the study on your own without an expert opinion. This can be tedious and time consuming.

Synopses of studies (above studies)

Clinical question

I want to find the latest treatment for my patient's illness but: (1) do not have the time to read the study thoroughly, and/or (2) do not feel that I have the expertise to interpret the information in the article. Where should I look for this information?

Answer

Using resources that summarise single studies would be the best place to look. Some of these resources include appraisal and application of the literature.

Sample resources

ACPJournalWise; Evidence-Based Medicine; McMaster PLUS Database; Journal Watch.

Strengths

The studies chosen for synthesis are usually of higher quality, summarised for the reader and have commentary to help interpret the findings in the appropriate clinical context.

Weaknesses

Not every study has a synopsis, and thus the list of studies with a summary is not extensive.

Syntheses (step above synopses of studies)

Clinical question

I know there is a lot of literature about my clinical question but is there a resource I can use that integrates all of this information and provides recommendations given the data?

Answer

Systematic reviews with or without meta-analyses are ideally suited for this type of questioning.

Sample resources

PubMed; The Cochrane Library; DynaMed; Database of Abstracts of Reviews of Effects (DARE); The Campbell Library; Agency for Healthcare Research and Quality (AHRQ).

Strengths

Systematic reviews: (1) integrate existing information and thus provide increased power and precision or effect size; (2) establish whether findings are consistent and can be generalised; (3) assess consistency of relationships (direction and magnitude of the outcome) given the variability in study protocols; (4) explain data inconsistencies and conflicts and (5) can reduce random and systematic errors (bias) of single studies by using meta-analytic techniques to combine data.

Weaknesses

Systematic reviews: (1) can be very long and difficult to read; (2) do not control for sources of bias; (3) can result in bad statistical outcomes if poorly designed/analysed studies are combined (garbage-in and garbage-out); (4) can result in exaggerated outcomes if only published studies are used (ie, bias against negative or unpublished results) and (5) can be misleading if conducted with an agenda-driven bias.

Synopses of syntheses (step above syntheses)

Clinical question

I know there is a lot of literature about my question but I do not want to read through an entire systematic review to determine the evidence. Where should I look for this information?

Answer

Use resources that provide a synopsis of syntheses.

Sample resources

ACPJournalWise; Evidence-Based Medicine; DARE; DynaMed; Journal Watch; Evidence-Based Mental Health; Evidence-Based Nursing; AHRQ; Bandolier.

Strengths

These synopses provide a summary of a systematic review with clinical implications and often review the methodological rigour of the studies included.

Weaknesses

These synopses may not be very current as it may take some time for a synopsis to be conducted and published.

Summaries (step above synopses of syntheses)

Clinical question

I just want to apply the evidence for my patients when the topic arises. Where can I go to find the clinical bottom line?

Answer

Look for summaries that provide evidence-based decision clinical practice guidelines.

Sample resources

National Guidelines Clearninghouse; Clinical Evidence; ACP's Physicians’ Information and Education Resource (PIER); UpToDate; AHRQ; Skinsight; GIDEON.

Strengths

These summaries often provide levels of evidence to help determine the strength of the evidence for a particular therapy, screening, etc.

Weaknesses

Summaries need to be updated often as evidence changes. Different practice guidelines may exist depending on the organisation that establishes the guidelines. Thus, it may be difficult to decide on the best practice given different guidelines.

Systems (top of pyramid)

Clinical question

How can I keep up with the guidelines for each of my individual patients?

Answer

Electronic health records that have computerised decision support systems would be one way to keep up-to-date and evidence-based for each patient in real time.

Sample resources

These systems are evolving and not currently widespread. The most common example is seen in the US Veteran's Administration electronic medical record.

Strengths

A system would include a custom-fitted health plan for each patient based on their individual characteristics and health status.

Weaknesses

The system itself would need to be upgraded regularly as evidence-based medical decisions change. One potential draw-back is that a system may not be able to consider patient preferences in decision-making.

Conclusions

For readers with limited time, using search engines to help find the best available evidence may be appealing. Sites such as Google have a custom search link one can use http://www.google.com/cse/home?cx=004326897958477606950%3Adjcbsrxkatm. Google also has Google Scholar that can help with medical literature searches. Searchable databases include the TRIP database (http://www.tripdatabase.com), Evidence-Based Medicine Reviews (http://www.ovid.com/site/catalog/DataBase/904.jsp), the Centre for Reviews and Dissemination (http://www.york.ac.uk/inst/crd/index.htm) and SUMSearch 2 (http://sumsearch.org). Unfortunately, some of these search engines and the resources reviewed require a paid subscription.

While we all await the day for instant answers to our clinical questions, we currently must use the best evidence at the most specific level available when searching the medical literature. Developing a familiarity with one or two resources at each step of the hierarchy can only help improve our efficiency and effectiveness during our clinical inquiries.

Footnotes

  • Competing interests None.

  • Correction notice This article has been corrected since it was published Online First. The Introduction section has been added into the article.

Reference