Table 1

Levels of evidence for treatment effect

Level I
Randomized trials with low false positive (α) and low false

negative (β) error (ie high power)




Level II
Randomized trials with high α error or low power




Level III
Non-randomized concurrent cohort studies




Level IV
Non-randomized historic cohort studies




Level V
Case series

Adapted from Cook et al [2].

Kellum Critical Care 1997 1:53   doi:10.1186/cc103