Equivocal Literature. The literature cannot
determine whether there are beneficial or harmful relationships
among clinical interventions and clinical outcomes.
Level 1: Meta-analysis did not find significant differences
among groups or conditions.
Level 2: The number of studies is insufficient to conduct
meta-analysis, and (1) randomized controlled trials have not
found significant differences among groups or conditions or
(2) randomized controlled trials report inconsistent findings.
Level 3: Observational studies report inconsistent findings
or do not permit inference of beneficial or harmful relationships.