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Evidence-Based Medicine: Finding Best Evidence

A guide to tools and resources on the topic of Evidence-Based Medicine

The 4S Approach

Textbooks, which may become inaccurate very quickly, are not considered a valuable source of evidence for EBM. To find best evidence, consider using the "4S" Approach:

  • Systems
  • Synopses
  • Syntheses
  • Studies

Picture these terms in a pyramid, with "Systems" at the top and "Studies" at the base; the higher in the pyramid, the more ideal the source of evidence.



Systems are considered the ideal source of best evidence. They summarize important evidence about clinical problems from multiple sources and are frequently revised. Effective systems give clear, reproducible descriptions of procedures and cite evidence in support of their summaries. It is hoped that in the future, these systems will be linked to individual patient medical records to inform decisions.

The most popular systems are BMJ Publishing Group's Clinical Evidence, UptoDate, and Ovid's Evidence Based Medicine Review. 


Synopses are condensed summaries of individual studies or reviews; ideally, only the information necessary to support clinical action is included in a synopsis. Summaries and abstracts in journals like Evidence Based Medicine and ACP Journal Club represent types of synopses. 


Syntheses are also called "systematic reviews". Systematic reviews are comprehensive literature searches that summarize studies and their evidence. While exhaustive, syntheses are difficult to use quickly to make clinical decisions. The best-known source for syntheses is the Cochrane Library.


Studies can be located through online databases and search engines; using studies as a source of evidence typically indicates that the publication is so new that the information will not yet appear in a synthesis or synopsis. Because it takes time and significant analysis to determine best evidence from a study, such sources are typically considered a last resort in making clinical decisions.

Search Strategies

For every clinical questions needing an answer, you will have to determine the highest level of the pyramid that you can search. 

Use specific terms and MeSH terms

Utilize filters


Search PubMed, PubMed Health, Cochrane Library,