NASA Categories of Evidence comprise a matrix or scale denoting the sources of evidence provided in the Human Research Program's various evidence reports, and thus potentially their probative value and efficacy.NASA Categories of Evidence Authors in the Program were urged to label their evidence according to whether it was based on controlled experiments, observation, or expert opinion.
Broad "Experimental" Design TypeSilagy & Haines Levels of EvidenceNasa Categories of Evidence ControlledIa - Meta-analysis of randomized trials I - At least one randomized, controlled trialIb - At least one randomized trialIIa - At least one controlled study without randomization II - At least one controlled study without randomization, including cohort, case-control, or subject operating as own control.IIb - At least one other quasi-experimental studyObservationalIII - Non-experimental descriptive studies, e.g. comparative correlation or case studies.III - Non-experimental observations or comparative, correlation, and case or case-series studies.OpinionIV - Expert committee reports or opinions or clinical experiences of respected authorities.IV - Expert committee reports or opinions of respected authorities based on clinical experiences, bench research, or "first principles".
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