Table 5.

American Academy of Neurology criteria for classification of evidence in studies of causation (Gronseth GS, Cox J, Gloss D, et al. on behalf of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology. 2017. Clinical Practice Guideline Process Manual, 2017 ed. Minneapolis, MN: The American Academy of Neurology)

Classification	Criteria
I	Prospective cohort study with all relevant confounders controlled, masked or objective outcome assessments, and a) ≤ 2 primary outcomes, b) clearly defined inclusion/exclusion criteria c) ≥ 80% study completion rate.
II	Retrospective cohort study or case-control study meeting all other class I criteria.
III	Cohort study or case-control study meeting all class I or II criteria except a, b, or c above.
IV	Studies not meeting class I, II, or III criteria