Type

Strength

I

Strong evidence from at least one systematic review of multiple well-designed, randomized controlled trials.

II

Strong evidence from at least one properly designed, randomized controlled trial of appropriate size.

III

Evidence from well-designed trials without randomization, single group pre-post, cohort, time series, or matched case-control studies.

IV

Evidence from well-designed, non-experimental studies from more than one center or research group.

V