Table 2.

American Academy of Cerebral Palsy and Developmental Medicine (AACPDM) levels of evidence.

Levels of evidence	Study design
I	Systematic review of randomized controlled trials (RCT) Large RCT (with narrow confidence interval)
II	Smaller RCTs (with wider confidence intervals) Systematic reviews of cohort studies “Outcomes research” (very large ecologic studies)
III	Cohort studies (must have concurrent control group) Systematic reviews of case–control studies
IV	Case series Cohort study without concurrent control group (e.g., with historical control group) Case–control study
V	Expert opinion Case study or report Bench research Expert opinion based on theory or physiologic research Common sense/anecdotes