The strongest evidence is in the secondary or pre-appraised research.
The 6S model evidence pyramid
The pyramid is divided into levels with the strongest evidence at the top. Systems is not widely used. Begin with Summaries. 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.
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
Synopses of Syntheses
Syntheses (Systematic Reviews)
Synopses of Single Studies