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.
Summaries
Evidence-based guidelines – highest level in Summaries
Synopses of Syntheses
- ACP Journal Club (Evidence-Based Medicine Reviews (EBMR, Ovid menu)
- Database of Abstracts of Reviews of Effectiveness (DARE) (EBMR, Ovid menu)
Syntheses (Systematic Reviews)
- Cochrane Database of Systematic Reviews (EBMR, Ovid menu)
Synopses of Single Studies
- ACP Journal Club (EBMR, Ovid menu)