Melnyk and Fineout-Overhold [4] describe an evidence table where the level of evidence is as follows (from highest to lowest rank): Systematic review of multiple random controlled trials.

No serious adverse events were reported. Conclusion Six trials with high risk of bias showed level-3 or level-4 evidence in favour of stem cell injections in KOA. In the absence of high-level evidence ...

Objective To synthesise the evidence on the effects of physical activity ... online supplemental eFigure 3 and online supplemental eTable 4). Grade of recommendation: (A) Consistent level 1 studies.