Table 1.

ILCOR levels of evidence for therapeutic interventions

LOE 1	Randomized controlled trials (RCTs) or meta-analyses of RCTs
LOE 2	Studies using concurrent controls without true randomization or meta-analyses of such studies
LOE 3	Studies using retrospective controls
LOE 4	Studies without a control group (for example, cases series)
LOE 5	Studies not directly related to the specific population (for example, different patients, animal models, mechanical models, and so on)