The strongest evidence is in the secondary or pre-appraised research.
The 6S model evidence pyramid
DiCenso A, Bayley L, Haynes B. Accessing preappraised evidence: fine-tuning the 5S model into a 6S model, ACP J Club. 2009; Vol 151 Issue 3: p1
The pyramid is divided into levels with the strongest evidence at the top - start at the top and drill down
Begin with ‘Summaries’ as ‘Systems’ is not widely used. If you cannot find the information in ‘Summaries’ continue down the pyramid remembering that the strength of the evidence decreases as you go further down the pyramid.
Evidence-based guidelines – highest level in Summaries
Synopses of Syntheses
Syntheses (Systematic Reviews)
Synopses of Single Studies
Primary sources are single studies which have not been evaluated
Primary sources have their own hierarchy – see the pyramid below.
Match the publication type to the question being asked (Refer to the ‘Type of question table’ when choosing from this pyramid)
Single primary studies are found in the major medical, nursing and allied health databases - Medline (EBSCO or Ovid) and PubMed (the free version of Medline), Embase, CINAHL, PsycINFO.