Evidence Based Medicine
Hierarchy of evidence:
For ease of searching, sources of evidence below have been organised following the hierarchy determined by: the 5S or 5 sources model*
*Haynes RB. Of studies, syntheses, synopses, summaries, and systems: The "5S" evolution of information services for evidence-based healthcare decisions. Evid Based Med. 2006; 11:162-4
The most efficient sources for searching appear near the top. These sources should be consulted first as they contain pre-appraised summaries of individual studies, or syntheses of all available studies, on focused clinical topics. They may also include an assessment of the current state of the evidence in an area of clinical interest.
The lowest category in the hierarchy consists of a large number of individual primary studies. Each of these studies must be critically appraised for its applicability to a specific clinical scenario.
Summaries integrate the best available evidence from the lower categories, providing concise information on all aspects of patient management. They often take a condition-based orientation.
Single selected studies or systematic reviews that have been critically appraised and findings published as a single page summary or synopsis.
Syntheses: Systematic reviews and meta-analyses.
Original research inc. all types of trials, Controlled Trials, Clinical Trials, Cohort studies etc.
Randomized Controlled Trials (RCTs) are the highest level of evidence in this group. However, they may not be the most appropriate study design to answer your clinical question. Sometimes an observational/qualitative study is required (e.g. a question about patient/professional experiences, values, attitudes).