Skip to main content
. 2014 May 20;5:117. doi: 10.3389/fphar.2014.00117

Table 1.

Evidence level provided by epidemiological studies of different design.

Level of evidence Qualifying studies
I High quality, multicenter or single center, randomized controlled trial with adequate power: or systemic review of these studies
II Lesser quality, randomized controlled trial; prospective cohort study; or systemic review of these studies
III Retrospective comparative study; case-control study; or systemic review of these studies
IV Case series
V Expert opinion; case report or clinical example; or evidence based on physiology, bench research, or “first principles”